Most thing that is common with casino's are more of signup bonus or free spin I don't think creating an account without making use of it would get you any reward. They mostly sends you promotional emails and updates towards their platform or maybe when you make a deposit for the first time after leaving them for long could possibly get you some bonuses. But this is not certain that all casino will do that, it all depends.
All casinos will only send promotional notifications. Never offer directly bonus if someone doesn't make a deposit. The bonus is offered only to those who become inactive after playing for a long time on their site. Loyalty bonus is paid for them. Moreover, it is also true that some casinos offer free spins to attract customers where it is not possible to win anything big with those free spins. Because in some cases there is a limit on the winning amount against the spin.
Absolutely, though I am talking based on op post.
Same holds true for casinos, if you just register and leave they will send you some bonus to get you started playing.
This won't make any meaning at all, because since you are not a frequent users of those platform.
Maybe when you start making use of those platform then this could likely be possible but it is not a must for them to do it. However, there are some specific amount or range you should be given such bonuses. Some casino may decides to gift bonuses to those who are depositing up to $1k and above.