Most people who do things "just because", don't monetize because either it isn't possible or it isn't worth the effort. For a site with as much traffic as GP's, it's probably worth it. Regardless, anyone turning down that much revenue out of principle deserves a lot of credit.
Sometimes making money off of something turns out to be incompatible with enjoyment, and you find out too late.
Depends on the person, how slippery the slippery slope is, and the motivation for a particular project.
I could ask myself "how much money would I be willing to pay to bring benefit to a large number of people?" It's definitely nonzero. But that's not a great question, because we all hate losing stuff we have (and paying is losing). It's a lot easier psychologically to forgo getting the money in the first place.
(Note that I wouldn't be able to forgo that much money. Though I might be able to procrastinate throwing the monetization switch for a while. How long is relative to my level of privilege in my own finances.)
Agreed. Depends on the personal point of view for every individual, and that's the reason I commented as my "2c".
Personally, if I were the guy running the steamdb website I would have brought in the monetization aspect as quickly as possible, once I knew there was a lot of traffic coming in.