They also must have known how weak the evidence is that they used to prop up their 'effort preference' idea.
It is very easy for people to convince themselves of all sorts of ridiculous things, and that certainly applies to scientists as well. I would be surprised if Wallitt was saying, we know this isn't true and we have zero evidence but let's do it anyway. Maybe I'm naive about how venal people can be. I assume he convinced himself the evidence was robust enough to make the claims. Again, that's not a defense. The end result is the same--awful and horrible science. And it doesn't mean it's not research misconduct either.
For example, the letter I sent yesterday about the Hungarian cross-sectional study that made causal conclusions. I assume the investigators are so stupid that they actually believe their own ridiculous argument. I don't think they said, we know we can't do this, but we're doing it anyway. Not fixing something afterwards, of course, is or at least has a greater chance of being a venal response rather than just a self-deluded one. If that all makes any sense.