This kind of bonus is usually sent to players with low deposit activities to attract players to come back. When was your last deposit in Stake? If I can remember it correctly, I received similar email but it was for my Primedice account after more than a year with no deposits. Imo it should be working on any deposit, so you can receive the bonus with crypto deposit but ofc you can ask live support if you are not fully sure.
I assume that people who stop gambling could be considered into two parties. One of them is the person who started gambling somewhere else and if you offer them something to return then they will comeback and play here if they really want to, there is a chance you could convince these people to come back, maybe some of them won't, but some of them may come back.
But, there are also some people who do not have any money left and that is why they haven't been gambling here in a while, you can offer them the world and not get anything out of them considering they do not have any money at all, it is going to be something impossible for them in the end since they do not have money.