Simple past is the original past tense of the Germanic languages. It was once used in almost all cases in which we now use either simple past or present perfect. Composites with have (or originally also be, according to the verb) and the past participle are a relatively recent alternative that has been cropping up in most European languages. Originally this new style of expressing the past arose in situations in which it made literal sense: "I have eaten" means that I have something eaten in my stomach because at some point in the recent past I ate. It is still quite restricted in when you can use it. But it is very popular: Whenever you can use it, you must. This is the reason for the semantic distinction between simple past and present perfect.
It is likely that the situations in which the present perfect can (and therefore must) be used will continue to extend. This is an aspect of language change in which German is a bit faster, for a change: In colloquial German you can use the equivalent of the present perfect almost without any restrictions, at least in the south.
As far as I know, there used to be no past perfect and no past infinitive in the Germanic languages. But the present perfect provides an obvious way to construct these: If shifting "He has an apple" into the past yields "He had an apple", then obviously it should be possible to shift "He has been there" into the past in the same way: "He had been there". And if the infinitive in the first case is "to have an apple", then obviously in the second case we should be able to form the (past) infinitive as "to have been there".
At some point someone started doing this; then over the centuries it became standard. Once people became used to shifting present perfect back into the past, or to form past infinitives from it, they felt a pressing need to do the same with simple past constructions such as "He was there" or "He cooked". The most regular way of doing this would be to add the regular simple past ending -ed, yielding "He wased there" and "He cookeded". I think we can all feel that this would be much less acceptable than pretending we were starting with the present perfect instead of the simple past. When some people first did this, others probably cringed. Nowadays it's perfectly standard.