Maybe you have not been active on Stake for a long time that is why your bonus was very low.
I don't know the actual reason for this but I think if you are very active on the casino and you are getting this kind of bonus then you need to talk to the support so you can know the criteria they are using to rate users when it comes to bonus.
Perhaps it could enlighten you to understand what is behind the tiny bonus given to you for betting and how it can be improved.
It works the other way, casinos affers more bonus than the regular users to the dormant users to increase their engagement which is a strategy followed by most casino and I checked some replies and they stated that it is based on multiple factors for different kind of bonuses. Some will get higher bonus for being active in the recent days and some get more bonus for being not active at all just to reactivate and it's a mystery that we may not understand completely. But don't beat yourself up for receiving less than others, still getting one is better than not receiving at all.
Other possible reasons are that they opt out of promotional emails which means they won't receive such emails.