Well, the main reason is feeling a bit more secure that I can boot from Grub to a previous working state just in case. Though it can be done through Timeshift under EXT4, but seems to be lot of work to recover if system is unbootable.
And another reason (though might sound stupid) it is my personality! Yes! I tried BTRFS before (maybe September 2021 - you can search my old posts) and it gave me lots of problems. So, for my personality, this is a challenge I will never feel comfortable or settled unless I overcome it!
I assure you if I confronted Godzilla or the Incredible Hulk, I will never give up till I control them or I die! (Sounds stupid I know, especially I know there are bugs in BTRFS and EXT4 is more stable and mature.)