I am not a psychologist but I do a lot of research on weird groups with fringe beliefs. My understanding of the psychology here is that denialism comes from a specific place: the desire to not have to take action.
Decades ago, there were many excuses people could use to avoid having to take action. We're not sure yet, it could be a number of things, it won't interfere with business, it'll only affect other countries, the believers are just a bunch of reds.
Over time the excuses dropped away until now the only way to avoid having to take action is to go for straight-up total denialism. That's why more people are doing that.
We are not seeing denialists increase in number because fewer people believe the scientific evidence; we're seeing them increase in number because every position but those two is becoming untenable, and a lot of people just don't want to take the actions that they would have to take if they believed in the scientific evidence.
It's kinda the same pattern that we saw with creationists over the course of the 20th century.