It's easy to refactor (or completely rewrite) for whatever the hot new fad is when you're dealing with small codebases (<100k loc) that haven't been around very long and most likely won't continue to be in use for long. That's not productive when you're working on a product that has millions of lines of code and has been in use for years (and most likely will continue to be so).
It has nothing to do with "pointy haired bosses" - believe it or not a lot of us [enterprise developers] care more about actually getting stuff done then bragging to our friends how we're playing with whatever is hip this week.