They fell for a mixture of mostly money, but also flattery, and probably the odd honey-trap.
And I would add power. Money and power drive decisions, policy, and, I'm afraid, science. No doubt when these western scientists are given the red carpet when they go to China, and then more support when they return home, it's all pretty heady and addictive. "To hell with facts. I'm being rewarded so well for my science, it must be right! And if not, I'll make it so!" So flattery, yes, but flattery with some extras attached.
You've nailed it. In fact mostly power - exercising power - but also just feeling powerful - it's nice - that red carpet feeling of self-importance. It's how the Emperor's clothing crept in - or is it crept off? You go to nice conferences with other powerful, intelligent people where Bill Gates is giving a speech! Or Tedros! That's your tribe - the tribe upon whose shoulders falls the burden of steering the ship of humanity into the future for the common-good.
Once you've decided you're doing something for a 'higher truth', that's your license to lie about everything else. It's liberating - a moral un-mooring.
As we post the same people are busily justifying their deceit - with more deceit.
How to stop them getting away with it?
I'm not vindictive - not looking for life jail terms (not against it - not motivated by it) - but we can't carry on like the whole world of elites didn't just co-ordinately lie point blank to us to cover up a global atrocity - to protect the CCP.
That shit has gotta be unpacked - rebuilt - no matter how painful that is for the nice scientist people.