Very few people start with big transgressions. Usually stuff escalates.

It's why need systems that don't put humans in situations where bad behaviour is incentivised. Also why we need to be forgiving when someone comes forward with a small transgression, so people don't get stuck in escalating cycles.

I'm sure this guy did some solid research once upon a time.

I don't know about this specific case, but it's common for the big name researchers not to do any actual research or play any direct part in generating their images. That's often done by kids - 25 year old grad students, even 20 year old undergrads - or other trainees. Those people may not appreciate how easy it is to detect image manipulation and are still learning what kinds of 'refining' of imagery and datasets is acceptable, while the PI that pays their stipend or sponsors their visa rages at their inability to get an expected outcome or replicate a previous result.

Not saying there aren't people out there just flat-out frauding, but these are group projects with a structure of trust and pressure that can muddy assignment of culpability. Like any committee or corporate action, it can be tough to say that any one individual is the guilty party or which people where just going along with the group.

I don't think it is a "and then commit fraud". They only got caught for the recent stuff.