I think the answer is simpler: people care about their careers and their family first. Think, "If the data says something that gets in the way of my career well I don't care about the data."

Had the same problem when I was an economics researcher -- publication bias for what stakeholders want to hear (often the government) is rampant because that's where funding for the economics department mostly comes from.

We totally are, it's just that rationality is a tool, not a guide. If you want to work out the truth, rationality will help you do that, but if instead you want to justify a decision you already made, well, it'll help you do that too.

"Man is not a rational animal; he is a rationalizing animal."

-- Robert A. Heinlein, Tunnel in the Sky, 1955

A whole industry of emotional branding is thriving, systematically overloading our brains so it hurt to even think differently in the moment.

We are accepting a whole lot of assumptions every day.

or is it that psychologists feel that we aren't rational and use reason to justify this?

it isn't clear to me how the grounds for realizaing the theory are reconciliable with its conclusion

Thats because psychologists dont understand or choose to ignore how chemistry influences our personalities and emotions. An extremely simple example from the same medical/health profession is the use of SSRI's to make people feel happy. The legal system recognises how chemicals influence our feelings because of the laws that exists on illegal drugs or drink driving.

The definition of rational is being informed enough to know what said chemicals will do in the short term and long term in order to make an informed decision, but then I'm reminded we dont get taught any of the above unless we specialise at a Uni, so most people cant make any sort of informed decision.