This only happens when exiting the end via end/nether portal.
Not when entering, nor both ways between nether and overworld.

Having minecartMaxSpeed at 90 and below your velocity will not be lost.
At minecartMaxSpeed 91 and above you will come to a dead stop when exiting the end.

Reproduction Steps

• Build a 250 block long powered rail track leading up to the exit portal
• Set minecartMaxSpeed to 91
• Enter a minecart at the end of the track and ride it towards the exit portal
  video_demo(1).mp4

Here's the world so you don't have to build the reproduction setup manually
MC-275558 Repo.zip

Observed Results

• Your velocity is set to 0 when you arrive in the overworld

Expected Results

• Your velocity would not be lost