In general, the reason is simple: python programmers tend not to worry too much about the language, although there's a fair bit of fretfulness about the folks trying to do functional stuff in Python, or people who want Python to be LISP. But apart from those groups, pretty much everybody else just sits down and writes their code, and generally pretty soon forgets they're writing in any language in particular, they just sort of churn out code that pretty much works as expected.
And that's really the point of Python. You stop noticing it after a while. It doesn't reward extremely subtle cleverness (much) and it doesn't severely punish stupidity, it just sort of does what you expect, and pretty soon there's your working application, stable, maintainable and clean(ish.)
I can't give a language higher praise than "it doesn't get under foot, and there are very few nasty surprises."
Python. Unless there's a specific reason to do something else.
PS: web frameworks in Python kind of suck because they're mostly a bit abstract. You might well wind up bolting together something dirty for your own needs.