Why is Progressive Enhancement so unpopular?

A little earlier today, having read how Sky broadband had blocked the jQuery CDN I tweeted

Sky broadband erroneously blocks http://t.co/5i7EXxYlDy and that’s why we don’t depend on JavaScript, kids.

— Drew McLellan (@drewm) January 27, 2014

To which many responded this is why we don’t rely on CDNs and how you can (shock, horror) even host your own JavaScript fallback and how you make a hole at each end of the shell and suck with a straw. In order to clarify the problem, I followed up with

What the Sky/jQuery...