Voyager was lost in 2371, now I realize that for a long time the Alpha Quadrant probably had no idea where Voyager was or if it was even still operating, but at some point during the series they made contact through a communication relay network. At that point they must have had a pretty fair idea as to where Voyager was, why were they unable to send a Galaxy-class ship to retrieve them?
The communications network you're referring to covered an extemely large area of the galaxy. Although Star Fleet knew where Voyager was it would have been a very large undertaking to send a rescue mission to redevous with Voyager, with odds of success likely nearly as poor as Voyager's were of returning on their own. Aside from that, had Voyager found their own way back (as they did) then Star Fleet would have still had another ship left in deep space, potentially needing its own rescue (which if they had sent a Galaxy class ship would have meant nearly 10 times the number of people on Voyager in danger).
Starfleet had no idea what happened to Voyager in the Badlands. They searched for several months with no trace, and assumed the ship was lost.
It wasn't until "Message in a Bottle" that they finally learned of Voyager's existence in the Delta quadrant. Once they did, they immediately initiated the Pathfinder Project to figure out a way to bring them back home.
In "Pathfinder", we learn that Starfleet has spent several months and considerable amount of resources trying to figure out a way to bring them back home quickly. This project was initially a failure, namely because any ship sent out to meet Voyager would have to make the return trip home: potentially risking the lives of a whole other crew while taking years to complete.
So Starfleet did the next best thing, with the help of Voyager, by establishing regular contact. Voyager gets several lucky breaks via technology way beyond Federation knowledge and winds up on the verge of the beta quadrant by after only 7 years.
In the end, it took a future Captain Janeway and the disruption of the Borg transwarp network to finally bring Voyager back into Federation space. We learn in "Endgame" had that not happened, it would've taken another 16 years. So even at the end of their journey, it would've taken Starfleet 8 years to meet Voyager even halfway, and another 8 years to get back. Endangering the lives of another crew for that long would not have been considered an acceptable risk.
Sending a ship to meet Voyager would not have made the return trip any faster. That's why I never understood the part when somebody said that 2 ships had been sent to meet Voyager and they would meet "in a few years". That's bad writing at best. There's no way sending a ship (except something like the Dauntless, faster than a speeding bullet) would have helped.