No, there are no specific reasons. If you need something in a configuration, simply add it: https://github.com/armbian/build/blob/master/config/kernel/linux-rockchip-default.config
and submit changed config. Changes come to the beta repository in 24h hours, if build succeeds, and in next major release when it's out.
Rockchip kernel is under heavy changes and there are some known ongoing issues. I can't give you a warranty that this beta kernel will work as expected. ATM. Check this: https://forum.armbian.com/topic/7498-nanopc-t4/?tab=comments#comment-56635
If you don't need any video-related features, better move to a modern kernel and edit this configuration: https://github.com/armbian/build/blob/master/config/kernel/linux-rockchip-next.config if things you need are not present.