If you don't subscribe to the logic and end-user benefits of progressive enhancement, there are probably many things about HTML+CSS+JavaScript that you don't like.

However, what are the arguments for what you are asking for besides easier short-term development practices? And, as said above, there's nothing stopping you from building your webpages that way (especially a “widget” that is self-contained). It works that way as well. How does this make HTML+CSS+JavaScript broken? If anything it is very resilient to different coding practices.