why does disney put easter eggs in there kids movies, such as monsters inc?

Everyone wants to make kids think they are so smart, when most kids are really dumber than a post. It's just another way Disney makes money.

The animators enjoy doing it as callbacks to their earlier work. When you work so hard movies like these, it's natural that you want to celebrate it in your next work.

Just for fun.
Don't you ever do anything just for fun?
Also, they know that a lot of people enjoy noticing them.

Because they can there is no point.