Firstly, the aim is that Questions and Answers on this site are as widely applicable as possible. The extra packages that you load, may not be needed at all by another user. For example, you may be writing you document in Czech, but loading
babel with the
czech option is not the cause of the problem you are having, and the answer given will thus help a person writing in English (with
babel) or Swedish (with a different
babel option) too. In particular, your standard lists of packages is not the same list another person uses, this is (partly) why they are packages rather part of the core of LaTeX.
Removing extra packages makes example coder shorter and clearer. Thus it will be easier for someone visiting the site later to decide whether the question answer are relevant to their problem.
Also removing unnecessary packages is helpful in locating, where the problem may lie, and is a useful debugging technique in itself. There may indeed be a bug in a package, or there may be a problem with loading order.
In any case, in the act of creating a MWE you may well reduce the code to the point where you can see the error or solution yourself, and so asking on this site is no longer necessary.