I would like to point to the fact that when Luke is escaping with Darth Vader, the battle already took a huge step in favor of the alliance. The Shield generator on Endor was destroyed where every man inside the Death Star knew it wasn't fully defensively operational yet. The Star Destroyer crashed into the Death Star moments before.
I can imagine whenever you see the battle take a new direction that isn't in your favor, you will try to survive and let us not forget that the first Death Star was taken down too.
From the script on IMSDB:
130 INT DEATH STAR - MAIN DOCKING BAY
Chaos. For the first time, the Death Star is rocked by explosions as the Rebel fleet, no longer backed against a wall, zooms over, unloading a heavy barrage. Imperial troops run in all directions, confused and desperate to escape.
In the midst of this uproar, Luke is trying to carry the enormous deadweight of his father's weakening body toward an Imperial shuttle. Finally, Luke collapses from the strain. The explosions grow louder as Vader draws him closer.
EDIT: @Boelabaal for why he didn't force lifted him:
EMPEROR Now, young Skywalker...you will die.
Although it would not have seemed possible, the outpouring of bolts
from the Emperor's fingers actually increases in intensity, the sound
screaming through the room. Luke's body writhes in pain.
Vader grabs the Emperor from behind, fighting for control of the robed
figure despite the Dark Lord's weakened body and gravely weakened arm.
The Emperor struggles in his embrace, his bolt-shooting hands now
lifted high, away from Luke. Now the white lightning arcs back to
strike at Vader. He stumbles with his load as the sparks rain off his
helmet and flow down over his black cape. He holds his evil master
high over his head and walks to the edge of the abyss at the central
core of the throne room. With one final burst of his once awesome
strength, Darth Vader hurls the Emperor's body into the bottomless
The Emperor's body spins helplessly into the void, arcing as it falls
into the abyss. Finally, when the body is far down the shaft, it
explodes, creating a rush of air through the room.Vader's cape is
whipped by the wind and he staggers, and collapses toward the
bottomless hole. Luke crawls to his father's side and pulls him away
from the edge of the abyss to safety. Both the young Jedi and the
giant warrior are too weak to move.