I don't think that many IIT students hate "private engineering colleges."
The reason someone should dislike "private engineering colleges" is because the only thing that is reasonable in their name is "private". There is neither "engineering" in these establishments, nor are they "colleges" as the primary goal is making money for the owners, not "education."
The reason that these "colleges" are getting away with such low standards is because everybody wants to be an "engineer" when they don't even like engineering or science for that matter.
There are some exceptions, of course.