Totally agree with what OP has written!
Something that might be unpopular opinion, these amateur leagues or lower leagues tend to be more prone to match fixing as players will do anything for their financial wellbeing because the sport does get them paid fairly...even if it's not match fixing at the worst players don't keep themselves in their best sharp because of several jobs taken as pointed out.
But on the bright side, lower leagues are not a bad place to catch some upsets

Yeah, if only they are being paid too.
But let's face it, the players of the NCAA will still play hard because they have a goal. Either in the NBA or other sports where they will be paid better if they are scouted. So, match-fixing could exist there but there are also the teams that will play really hard to win their respective games or show good stats so that they can get the highest draft pick when the time is ripe.
Being a professional in the entertainment industry like basketball is paid quite high today. They will do their best to achieve that so let's also consider that while betting for the NCAA. However, I really like the idea that they are also being funded by online sports bookies because they are making money out of them in betting.