But lots of countries don't have long term tourist visas. Actually, more accurately, almost no countries do. Tourist visas aren't intended for long term stay. Just try staying in the USA on a tourist visa long term. As for a visa category for someone who has the money and doesn't need to work, it does already exist. It's call the Thailand Elite visa. Several people I know including my partner have it. We played by the rules for someone under 50 that wants to be able to stay long term without hassle.
That same argument could be made against any country that requires a visa or special permission to enter, which is most of the world for certain nationalities. Get the right visa for your intended stay. If the US denies your visa (as they do all the time for many people trying to get visas to enter), can the person just scream indignantly that the US doesn't want their money? That's a silly argument to justify allowing people into a country if they don't meet the reason for the entry they are seeking.
"half of the people were on visa runs and about half of them were in the same situation as him", then it is no wonder that Immigration was denying so many people. So many people that were clearly not genuine tourists, and I'm not surprised that they would be much more strict. Interesting that the minute Cambodia opens, there is such a mad rush to do visa runs there. Probably wasn't wise to think that immigration wouldn't notice.
Why are you trying to sound like I made any judgement about whether he should be allowed in? All I did was say why immigration would have denied him. He's clearly not a tourist, that's all I am saying, and he tried to get away with entering by an entry intended for short-term tourists. He didn't qualify and is hardly the first person to get in trouble with immigration for this. As I see the moderators of this forum always repeat: "get the right visa for your intended purpose and length of stay." Who said anything about wanting him to spend his money here?
I think you kind of answered yourself why they would deny him. He's stayed in the country for 2 years and thought he could leave on a visa run and be allowed back in when he clearly isn't a tourist.