Answer is Reading Comprehension
Many gambler playing just into those gambling casino without even having time reading with the terms and conditions such as the faqs. As long as they see the bonuses or ever that requires to play, they quickly deposit and play, and after they win a good profit, they make a withdrawal immediately it's pretty suspicious to the casino too if this happen because the account does not even last long for a week to play and win and make an instant withdrawal they might probably tag as abusing the system.
I disagree with the part where you talk about reading comprehension, but I agree with the part where you say about people rushing to want the bonus, and a sad scenario where people's greed blinds them, but the problem of complaints has to do with the fact that casinos are scams, there are many casinos that have problems when paying, especially when the person makes a small deposit and manages to win a lot of money at the casino, the casino is in pain because it feels like it wants to pay a lot of money to the customer
for example there are many cases in which people make a deposit of 500$ and manage to win and are left with 2500$ or more, and the casino starts to see that it will have a loss of 2000$ if they pay the customer the 2500$, so the casino starts telling stories like: "the customer needs to do KYC, well the customer needs to wait for the casino to do investigations because they suspect many accounts
If they don't research before joining the casino, they will be scammed and regret it.
about this issue of doing research before creating an account at the casino, what has been happening is that people can even do some research, but they don't do the research well, for example, the person can go to google and then the person writes: "good casinos" and will click on the first link that appears, and if it is a link from a site that has no ethics and honesty, that person will think that all casinos on that site are honest while in fact it is a site paid by casinos and post positive reviews