I had this problem with XUI (and even Madrobby's brilliant Emile - although that's mostly a proof of concept). The library is just beneath what I consider necessary in terms of flexibility and robustness to be usable in production. Like no error handler in Zepto Ajax - seriously? An Ajax request will never fail... on mobile!? And this could be my perception - and I could be completely wrong - but when something is marketed as 'in only 2K!' or 'in under 50 lines!' there's a discouraging resistence to adding code in order to keep those metrics.

On the other hand, most micro-frameworks require the user to take more responsibility for making sure things don't break - which could mean lighter code... a good thing for mobile. For example, Emile does a fine job of tweening integers or colors, but watchout for inherited values - like fontWeight 'normal'. So the user has to take the extra step of defaulting the styles to values the script can work with.