I read this short story about 30-40 years ago.
"The Climbing Wave", a novella by Marion Zimmer Bradley, also the answer to this more recent question; first published in The Magazine of Fantasy and
Science Fiction, February 1955, available at the Internet Archive.
A rocket crashes back to earth centuries after the earth has gone through a form of destruction with few survivors.
There is no crash; first the shuttlecraft and then the big starship land safely on the Earth. They are coming from a colony on a planet of Theta Centauri which had been founded by the crew of the first starship from Earth, which was damaged in a crash landing:
It had taken four generations for the stranded crew of the original ship, the Starward, to repair the hyperdrives smashed in landing, and to wrest from the soil of Θ Centauri fourth planet — Terra Two, they called it — enough cerberum to take a pilot crew back to earth with news of their success. A hundred and thirty years, subjective time. Taking account of the time-lags engendered by their hyperspeeds, it was entirely possible that
four or five hundred years had elapsed, objectively, on the planet their ancestors had left.
The Earth has suffered an overpopulation crisis sometime in the past; the colonies on Mars and Venus have been abandoned, the cities have been abandoned, and the reduced population lives a decentralized life in small villages. Earth native Hard Frobisher explains:
Probably the overpopulation reached such extremes—the solar system as a whole, of course, since Earth had to feed Mars and Venus too—that for one or two whole generations, every able-bodied man and woman had to put all his efforts into food-making instead of theoretical astronomy or whatever they called it. And by the time they had that problem solved, people were thinking of science in terms of human benefits, and probably realized that their resources could be handled more efficiently here on Earth.
One of the rocket men tries to reintroduce technology, only to be shut out by the locals. After time, most reintegrate back into society, except for him.
That would be Brian Kearns (technically a hyperdrive technician, not a rocket man), former Captain of the starship Homeward. He and his partner stay aboard the starship while the rest of the crew move into the village:
"Brian is crazy!" Paula said emphatically. "Ellie—is it really true that you and Brian will go on living in the Homeward?" She glanced distastefully at the black mass of the starship, and went on, "Why do you stand for it?"
"I'd live with Brian in a worn-out hydroponics tank, Paula. You would too, if it were Tom," Ellie said wearily. "And Brian's right, some one should keep the ship from being dismantled. Any of you had the same choice."
A day comes when one of the females is due to give birth and a group is being gathered to go to her. The former rocketman wonders how they will travel quick enough to be at the birth.
Paula is having a problem with her pregnancy, apparently related to conceiving in free fall:
"You're right there's something wrong," he raged, and advanced on Frobisher so violently that the old man retreated a step or two. "I've got a girl on my hands who looks as if she were going to die," Brian roared, "and I want to know where on this devil-ridden planet you packed Tom off to, and where Marcia's gone! And then I want to know if there's a decent medical man anywhere in this damned backward dark-ages Utopia of yours!"
A local pulls an helicopter out of a barn, to the rocketman's surprise.
"I doubt if you'd understand," Brian snapped, but Frobisher said
steadily, "I suppose it's the gravity sickness. Tom mentioned it
before he left. It's easy to get hold of him. Destry—" He turned to
the boy in the doorway. "Quick, go down and get the Center on the
wire. Tell them to fly Mellen back here, inside an hour if they can.
And—where's your father, Destry? This sounds like something for him."
[. . . .]
"What the—what the hell—!" Brian started, but
Destry was already hurrying down a flight of stairs. Hard Frobisher
put a compulsive hand on Brian's shoulder and shoved him after the
boy. Brian stumbled on the steps and blinked in the raw light of an
electric arc-bulb. On a rough wood workbench, with Destry's notebooks
and a few ordinary boy-type oddments, the stupefied Brian recognized
what was unmistakably a radio transmitter. And not a simple one.
Destry was already adjusting earphones and making a careful
calibration of an instrument which looked handmade but incredibly
delicate. He moved a key and said in a hurried voice, "Marilla Center,
please, second-class priority, personal. Hello—Betty? You've got a man
in the Center working on radio? Mellen? That's the man. This is Destry
Frobisher talking from Norten. Fly him over here—as fast as you can
make it. His wife's ill—yes, I know, but it's a special case. Thanks—"
A long pause. "Thanks again, but we'll manage. Look, Betty, I have to
get Slayton. Clear the stations, will you?" Another pause, and he
said. "My father. Why? Oh—thanks, Betty, thanks a lot. Tell them we'll
bring a plane over there for him." He closed the key and ripped off
the headphone, standing up, and Brian exploded again.
what's going on?" he demanded. "What kind of a bluff have you people
been putting up on us?"
The answer to his question: just because we have technology capacity, doesn't mean we have to use it.
"Listen, Kearns," Frobisher said abruptly, "you've been jumping to conclusions all along. Now don't jump to another one, that we've been bluffing, and concealing our civilization from you. We live the way we like to live."
"But radio—planes—you have all those things, and yet—"
Frobisher said, with barely concealed disgust, "You have the Barbarian viewpoint, I see. Radio, for instance. We use it for emergency needs. The Barbarians used to listen to keep from doing things—I know, they even had radio with pictures, and used to sit and listen and look at other people doing things instead of doing them themselves. Of course, they had rather primitive lives—"
"Primitive!" Brian interrupted. "You have airplanes and yet people walk—"
Frobisher said irritably, "Why not? Where is there to go in such a hurry—as long as we have fast transport for those few times when it is really necessary?"