This has been studied, and the ‘temporarily embarrassed millionaires’ idea is actually wrong.

The real reason is because some people (especially conservatives, because it’s a core part of conservative ideology) believe that in order for society to work, a hierarchy must be maintained wherein the ‘deserving’ are at the top, and everyone else is in their rightful place. Any threat to the natural hierarchy will undo the societal order and bring chaos and carnage.

This is why Obama becoming president was such an affront – because his presence outside his ‘rightful place’ was an existential threat to the natural order.

This belief has its roots way back when feudalism began to fail and the moneyed classes needed to find a new way to retain their power – both capitalism and conservatism were born at that time, with ideologies shifting from birthright to ‘earned’ status, which enshrined the haves and have-nots into literally sacred structures of meritocracy and social darwinism, and colonialists specifically fostered strict adherence to the social order. It became ingrained culturally that adhering to your station, whatever it is, is crucial for society to function. That there’s honour in being a cog in the machine, and that not accepting your lot in life is a danger to everyone. (eta: this is mostly subconscious, but you can see it if you ask ‘why’ enough times of someone who idolises Musk, for example. You’ll eventually whittle them down to these themes.)

That’s a nutshell view of a complicated topic, but these people don’t believe they’ll strike gold one day. They believe people who are rich deserve to be treated as kings, for the same reason monarchist peasants did.