I think it's because bitcoin is a relatively new concept that they have a difficult time wrapping their heads around. But they typically use fiat to make more fiat, introducing a crypto currency accepted globally undermines their purchasing power by taking away their fiat demand.
It's just like you said.
Many of them were negative at first but then changed their minds. The guys from Shark Tank are one of those. Mark Cuban thought it to be a ponzi scheme at first. I don't remember exactly but he said something like that about 5 years ago and now he owns some bitcoins. Kevin O'Leary said in 2019 that bitcoin is useless and now he's planning to invest in green mining.
These guys need a bit more time than we do, they're a bit slow and scared because they've seen many scammers in their line of work
