In strictly rational terms, it almost always makes sense. Even late funding round startups are risky -- when you have that kind of risk, the sanest thing you can do is to diversify early and often. Losing half of your potential future payout is nothing if you can exchange it for guaranteed middle-class lifestyle (or the funding for your next startup...).
Compound that with the fact that the utility of cash is, like the value of health an integral over time and you have more reason still to cash out early. Every if the utility were the same, five extra years of your life with the end-cash is five extra years of utility.
I get your point about pump and dump and if it was a no-name hustler ringing up a round for a just-arrived company I'd understand that but none of these companies ever are. I feel there's something deeper driving the reaction - it seems more resentful than rational.
Assuming I've done my due diligence on the dedication of the team, the last thing I want is for a founder to be focused on personal finances. Otherwise, they might be too focused on immediate monetization instead of growth.
If the founder has all their wealth tied up in the company, they might be more likely to manipulate to sell the company early to make themselves a multi-millionaire.
If you give them a bit of an exit, they then have more motivation to try and build the really really large company.