Marketplace requirements are another problem. Authors have to keep original Bootstrap CSS and JS files and overwrite them in separate files. It generates unnecessary CSS and JS code.
Jack of all trades, master of none.
Łukasz Holeczek

The reason for this is so when the new dot release of Bootstrap comes out, you can drop it in.

CoreUI looks cool, but I wonder how updating Bootstrap releases is going to work? Clearly you’re going to update manually — for a while. When you get bored will the whole thing become unusable because of all the custom surgery?