We don't have any kind of a clear picture of what caused the collapse. There wasn't a FAQ section on this until just now when I added it: the FAQ now has some excellent discussions by /u/Bentresh and /u/UndercoverClassicist, and also one by myself --

• How did the civilizations fall in the end of the Bronze Age?
• Did people realize they were part of a civilizational collapse during the bronze age collapse?
• Does anyone have any recommendations for books about the Bronze Age/ Bronze Age collapse
• When and how did we learn that the bronze age had really collapsed and was a thing and not just an imaginary folk idea like Atlantis?

Still, as FAQ sections go it's pretty short, so an additional expert answer would be most welcome if someone wants to write one.

As to your points about Troy: in the history of the Bronze Age collapse, Troy is just a footnote. The simplest way of dispelling the idea that a 'Trojan War' caused the collapse is probably just to point out that the historical Troy wasn't destroyed -- unlike many much more important centres -- and was inhabited continuously until around 950 BCE. That is, Troy carried on after the collapse for roughly as long as the USA has existed.

Some cities in the Mycenaean and Hittite arenas were indeed destroyed in the 'Bronze Age collapse', such as Mycenae, Pylos, Hattusa, and Ugarit. Others suffered an economic downturn, like Thebes, Miletos, and Knossos. Still others seem to have been unaffected, like Ephesos and Tarsos.

Wilusa/Troy definitely belongs in the second category: there was a downturn, followed by a gradual population decline, then resettlement in the 700s BCE. There's not much consistency about these things across the Mycenaean and Hittite worlds.

The idea that 'we now know Troy was real', with the implication that there was a time when we didn't know it was real, is untrue. There was never any uncertainty about the 'reality' of Troy, which was a thriving city and tourist site until around 500 CE. This changed when Schliemann made a concerted effort to conflate myth with reality, thereby making the reality seem doubtful. I wrote a short explanation here last year.