There is more reasons to steal a 20k$ watch than a 500K$ unsellable watch.
It's a pure vanity business anyway, the only reason to have a 500K$ watch is to show that you a have spent 500K$ on a watch. You get it stolen, insurances do their job, and you don't give a shit because you are a filthy rich asshole who didn't need that watch in the first place and will buy the next 500K$ watch to be made.
I think it is very plausible that he ran out of money. Purse+bonus was 310 000$ for the Jarzinho fight, which after all deductions comes down under 200K.
So 200K to last a year, it is still very comfortable, but if you expect to have a fight in the next 6months and it ends up taking a full year instead, it can easily run out. Especially when you support your family the other side of the atlantic. He doesn't have millions and btw, he doesn't have a 500K watch that's pure nonsense.
He didn't say he was broke, his main complaint was that he got left without fight for too long.
I respect your viewpoint.
Couple of items :
The Rozenstruik fight (in Florida May 9th 2020) (From the data that i've seen) he received total of U$320,000. Florida has zero state income tax, so federal tax calculations for a single man with no dependents gives his net income from that one fight should be :
US$223,000
PLUS : I would find it surprising if Ngannou didn't also have income from personal sponsorships, appearance money, that kind of thing. I am quite sure he has other income on top of fight money. For eg he DID do those TV commercials for a car dealership. So It's highly likely that his gross annual income for 2020 was far higher than the US$320,000 from the Rozenstruik fight.
Also, you can massively reduce your taxable amount if you setup an LLC Corporation and have training expenses, physiotherapists, nutrition cost, specialist treatments, transport to your "work" all written off as a tax-deductible item by your tax accountant. Mr Ngannou SHOULD be doing this. Whether he is or not, I do not know.
His income for the 2nd Miocic fight was FAR higher than the Rozenstruik fight and the data I'm seeing is US$580,000.
The watch thing: well someone posted a photo of THAT exact watch a Richard Mille RM11-02 Automatic Flyback Chronograph *on his wrist*. And I checked and the price I found was close enough to the stated $459,000 price --- I found US$504,000 price for that online. So he WAS wearing it. Draw your own conclusions. I guess it's possible he rented it, or was loaned it, don't know.