Summary:
Uncontrolled mobs (with the exception of a camel) cannot walk when a player sits on them. If you are sitting and do not control the mob like a strider, a pig, horses and their variants, llama, they remain in one place. At the same time, an uncontrollable camel (without a saddle) can walk with the player.

I expect that mobs on which you can ride should freely move when a player sits and does not control them (a mob without a saddle or a player does not have a stick with carrots/warped fungus). It would also remove the problem of parity (in Bedrock these mobs can walk freely with the player).

Or a camel should also not walk freely with the player, like the other mobs (if this behavior has some sense).

Steps to reproduce:

1. Summon a horse.

   /summon horse ~ ~ ~ {Tame:1b}

2. Sit and wait a while.

   /summon camel

3. Sit and wait a while.

Observed results:
A camel in comparison with other mobs can walk with a player.

Expected results:
The camel will not walk with the player/All mobs will walk freely when the player sits and does not control them.