Languages change, get over it. "Proper" language is directly the result of the same things that you're complaining about happening over and over again.
If we actually stuck to a perfect defined grammer, language would never evolve
I've got years of linguistics background, nothing to get over here.
The interesting thing you may or may not know is that this use of a past participle for a simple past actually has become normalized, in the languages change sense, in Russian, for one example. In English, it's usually less educated or second language acquisition speakers who make that substitution.
If we actually stuck to a perfect defined grammer, language would never evolve