Why would someone prove security in the real-ideal model instead of Universal Composibility framework? I am somewhat confused in the reasons why one would use the real-ideal model instead of the universal composibility framework.

The UC framework seems to me, to provide a much stronger definition of security. Is there some explanation to this?
Try to prove something non-trivial using the universal composability framework and you will quickly understand why few people use it.

EDIT: Snide remarks aside, it is pretty widely acknowledge that universal composability is really hard to use in papers. It's even hard to typeset - I've seen proofs with UC functionalities that don't fit on a single page! A colleague of mine has said that proving non-trivial things using UC is like writing a web server in assembly language. 

Aside from the practical difficulty of writing proofs with it, there's a more fundamental difference between UC and the real-ideal paradigm: the latter has an intuitive philosophical appeal that comports with the way people think about security. The former doesn't have the same "interpretability" IMO.