I think that this situation has developed due to the fact that the main goal was gambling, not bonuses. The one who hunts for these bonuses, first of all, does a thorough research of each casino in which he is going to register. I'm not sure, but it is possible that they have some kind of checklists and tables for calculating possible profits and some solutions for maximizing it.
But for an ordinary player, getting bonuses can be a problem - the casino is not interested in providing all the information on one page, so the player must do a big research and analyze the results, otherwise he will lose bonuses due to some restrictions that he did not read.
You mean to say that it is developed because casino owners know that many gamblers are only after the money or at the bonus so they sometimes mislead them with promising words but the terms are confusing when you are about to try them so that you won't end up with a win but you can lose more money in the process of trying to get those small bonuses.
For those who are bonus hunters, those guys are wise and yes they do have those items you list above because they want to make sure that they can successfully get the bonus. Ordinary players usually don't chase the bonuses because of the bad experience they have before.
No. I don`t mean it so categorically. The casino owners know, that if they write on the start page about bonuses with big letters it attracts attention. And the same time, if they write about smth you must to do if you want to get this bonus with small letters - the quantity of paid bonuses decrease seriosly. The common gambler doesn`t search these bonuses, he can get it accidentally. And the bonus hunter read everything before register and analyze what he has to get to get maximum bonuses.