Casinos are a business like any other and want to make money, so if a user is losing money and giving profit to the casino, they will want to keep hin in house as much as possible.
So yeah it makes sense to give this user more bonuses and rakebacks, because at the end he might still lose more and the profit keeps coming. But would you call this type of gambler vulnerable? Maybe he has fun gambling even if he loses money when the day ends.
The most important thing is to keep your customers because the house edge is enough for even some slow profit.
Their main target are gamblers that are consistent...I noticed that I was making use of a sports book consistently for over a year then I stopped for a while...i started getting sms notification from the sports book about different bonuses they were offering me and other offers as well...This tells you that the casino or bookie makes money off those that are consistently gambling, not per time gamblers