What could be the possible caused of the companies that are not giving the sign up Bonuses?
It's their choice not to give bonuses but usually, that is the practice bonuses are a means to try out games on their casinos if you win you have to deposit and wage to cash out that bonus, but if the company is already proven and established there's no need for sign up bonuses, as long as the casino has zero complaint and there are good feedbacks on their games there;s no need of sign up bonus.
There are still known or popular casinos which do still offer sign up bonuses which is of course having those kind of terms which you do really need to comply so that you would able to cash out and sometimes this would
really be talking about wagering requirement and some do really need for you to deposit before you could withdraw those winnings but of course with attached terms and conditions.
If Sign up bonuses do really exist on current site you are interested on then its up to your choice but dont get excited about it much.