I do not believe much in welcome bonuses, because when a deposit is made and if I make a profit I want to withdraw my money, but if a welcome bonus is accepted, it is conditioned on the fact that you have to make a high wager and sometimes make enormous amounts, And that doesn't make any sense to me, because it compromises the money and it can't be withdrawn, that's why I don't like to accept the welcome bonuses, there are many who say that they do, but that's leaving the money in the casino.
You are right. Many gamblers sign up on casinos, mostly new ones, and make deposits just because of their lucrative deposit bonuses. But they forget about the wagering requirement which, statistically, will drain their entire balance and they will end up with nothing to withdraw.
However, if you gamble for fun, you certainly will not refuse such offers because you made the deposit and don't mind losing it. So, the deposit bonus is just a chance to play more and stay longer on the casino.
Bonus is just an attraction of the casino to convince many players to gamble on their casino. It sounds good because of the term not knowing the rules associated with it. As you've said the wagering requirement needed to be able to withdraw the bonus is hard to fulfill but its not a pain to try right? But this is if you're playing for fun, otherwise it can get your funds busted. The reason why I prefer the casino's promotion over bonus because there's a chance to get real earnings through it.