Stake doesn't need to get customers back, they are growing more and more, at a rapid pace. Even if I wish for it to be a possibility

but increasing the existing weekly or monthly bonuses is the most unlikely thing to happen.

Could be, but still now they trying to get the customer back (the one who move, or not gambling anymore). I mean with those waggering promotion, and other seem like they're focused on there.
I think stake.com gives out bonuses randomly. I don't know what the purpose is, but I'm still actively betting on stake and am still subscribed to email. So it seems that this is not just to attract customers who have been inactive or moved to other gambling but indeed the bonus is given only to selected customers.