For some people, it's a job - finding new casinos and collecting as many bonuses as possible.
But I agree with you - for the average gambler, it's better not to try to get a big bonus from an unknown casino.
P.S. But even if I decide to visit such a casino, I'll ignore the bonuses, deposit only enough for a few games, and withdraw all my winnings.
The thing is that even if you won, you wouldn't be able to withdraw your winnings. The same goes for people for whom, as you said, "it's a job - finding new casinos and collecting as many bonuses as possible". It's a bad job. I'd even say it's not a job at all.
Find a good job, a job that you like, that you're one of the best at, and that pays decently. Then gamble for pleasure on top sites. Let gambling be your entertainment, not your job.
I call them bonus chasers. Their job is to find a new casino that offers bonuses and register to benefit from their offers. In my early days of gambling, I had a friend who was very skillful in that. He had many emails that he used to move from one casino to another. I can attest that he never benefited from his behavior because the wagering requirements are always high. Another problem such people don't consider is that they are exposing their personal details to multiple gambling platforms.
You have offered good advice that they should get a job or learn a skill that could contribute to having a good life instead of depending on gambling. Although we expect wins from gambling, it shouldn't be seen as a source of income.