Some level of personal guilt for continuing to exist in a system where fossil fuels are burned on their behalf and we often need to burn them ourselves to live a nornal life because the alternatives may barely exist. For example see DEI bike lanes in the states and the banning of them in ontario in canada thus promoting more car use and discourage/making it more dangerous to bike.

I just don’t understand what they stand to lose by admitting that humans have demonstrably increased the global temperatures.

Cars.

yeah, we didn't have fire season out here when i was growing up. we used to call it summer.

I think it's sunk cost. It's too late for them to admit that they were wrong because now it's too late to do anything. And admitting they were wrong this whole time would mean that there was time to do something and they squandered it to the detriment of not only their own descendants, but for literally every human on the planet.

Their ego will not allow it.