But my question remains - why so very few people understand that BTC has a finite supply that cannot be altered and should therefore be trusted to hold value more than infinitely supplied fiat.
Because most people are literally retarded.
I am using literally correctly here. Most people do not use the thinking part of their brain. They go by emotions, by whatever the crowd they hang out with deem acceptable.
It was the same with computers twenty years ago. Only nerds and losers were interested in them. Until it's suddenly acceptable to carry one around in your pocket.