I want to remap caps key to ESC and find BBT can't recognize caps, then I have tried karabiner elements and it works. My question is that why BBT can't recognize CAPs, and do developers have a plan to support this feature recently. ( I really don't want to use two softwares 
thx)
BTT can not do this, but you can do it in system preferences-> keyboard-> modifier keys
The system modifier keys only support map Caps Lock to Esc, it doesn't support map Esc to Caps. Could you support this in the future