So, if someone loses 100 bucks, casino gets couple bucks and gives the rest to investors as profit, if a person wins 100 bucks casino loses nothing but investors pay for that. It allows gamblers to gamble more because bankroll is usually bigger and it allows casinos to be able to spend their money on other stuff to get bigger and bigger instead of using their money as a bankroll for the casino. It is actually quite great for all parties involved.
speaking about the investment bankroll , in your example if someone loses 100 bucks casino gets its % straight after the bet usually
EV of the bet is taken into account and then the % they set for servicing bankroll is going to the site owner , i.e. 100$ loss expected value = 1$
1$ then is multiplied by the % the casino takes for managing bankroll , lets say its 35%
0.35$ goes to the owners , then the bet result is resolved and the bankroll gets the result of the bet win or lose , if the bet loses the investors get 1$ divided across them
according to their bankroll share
one more thing , usually all of the owners invest their money into bankroll too , you won't play at a dice that has only 0.02 btc bankroll, right?
and at first there won't be a que of investors , so you as an owner will HAVE to invest and risk
but investment bankrolls are beneficial for all of the parties involved : for the owners it allows to lessen the risks of getting bankrupt and close the site
for investors its an almost guaranteed longterm income , for gamblers its a sign of stability and increased max bet/ max win figures
if a site is trusted and good , investment model is the way to go