In any case, if by "major" you mean HUGE like godaddy or dreamhost? or some other unknown "big" player I have no knowledge of, it's because the majority of people do in fact use php for their applications. Ruby is popular only in the superCool underground world of github and company.
Point is the answer is in your question. Less people use node.js and rails, and django, so less providers are going to support it. Wide support = wide usage (im assuming)
Now if your question is why isn't there a one click install for local dev... i'm sure it exist in one form or another. For example Python has easy_install and pip. (pip install django)