The city was sparsely populated down to the 5th century BC, no clear reason is visible to archaeologists, whether due to plague, attacks of pirates, earthquakes, drought or famine are often the usual culprits.
I'm sure renovation is nothing new to our day, if it wasn't done at Mycenae there had to be good reason.
AKAIK Mycenae was at least partly occupied for most of the BCE centuries. Some Roman visitor(s) remarked in the first or second century AD that it was uninhabited. There have been so many theories about this that discussion can be repetitive, but it is still interesting.
As for "Dorians" overpowering a sophisticated civilization such as the Mycenaean, it is unlikely. What seems more likely is that they moved into areas that had been depopulated, or underpopulated, due to other reasons. I have tried to find record of volcanic activity that may have contributed to crop failure year after year, but I can't find anything probable. Food is the major thing that can cause desperate migration, so maybe the "collapse" was caused at least partly by that. Famine leads to reduced resistance to disease, etc., so as a consequence, plague or other epidemic events could have caused reduction in population to the point where agriculture would be so damaged, and the ability to defend would be so affected, that remaining was not an option or was at least very risky. It remains a mystery.
The arrivals from the north (Dorian/Ionian, or whoever) may have migrated in desperation for similar reasons. However, it does not seem likely that they were that numerous (similar to many of the barbarian migrations of 4th and 5th centuries AD). A large population requires food sources that can sustain it. The Balkans and the Pindus Mountains, where these new arrivals probably originated, are rugged terrain and difficult - 3000 years ago - to feed large numbers. In order to overpower the Mycenaean culture, an adversary would need greatly superior numbers for a swift conquest. I don't think that was the case.
Greece and the Aegean are geologically unstable, so some catastrophic series of seismic occurrences may have been a big reason. That just seems much too coincidental - all at once and everywhere.
I agree that abandonment and/or not reconstructing would have to have good reason. If Mycenae, or any of the Bronze Age sites, were advantageous places why would populations leave unless they could no longer feed themselves?