Not all the time, I played with the Moonbet recently and I managed to win their deposit bonus and able to withdraw it. For me they used it to attract players although some of them have difficult requirements probably it is to avoid abuse and also for the safety of their business, no one will run a promotion that the users will likely to win.
Actually this is quite reasonable considering that there are definitely conditions that must be set for this because this is their marketing, so it is certain that if you want to get this, it is clear that something must be presented first.
Attracting customers may be true but we can't do anything about it as long as it's a business and their rules don't violate the law then they do have the authority in my opinion.
the choice is whether we want to do it or not
Nice trying with moonbet with sign up bonus available to withdraw after winning on casino or sport betting games, but several gambling platform site make difficulty to withdraw fund reward achieve from bonus sign up, they will detect and looking for reason suspend our account with cheater reason although created one account only. I want to try with Moonbet but sign up bonus giving without make deposit or have rule with several fund deposit to earn bonus sign up.