A lot of people don’t like change, and Skyriding does feel strange! They can turn it off in multiple places. Help your friends learn how to do that if they are confused.
- Top of the mount journal is a spell to change it. Looks like a winged circle.
- Same spell can be put on your action bars and is default placed there when you log in if you have an open action bar spot.
- Probably in your spell book too but I have not looked.
If someone wants to quit over increased capacity, with the option to turn it off, that seems a bit dramatic to me.
If someone does not like it, click the button to turn it off. This one 
The only limitation is that the Expansion, War Within, has Dragonriding/Skyfling as default until max level like Dragonflight did. Old zones are all an easy toggle and flying is now available in old zones from level 10.