Which casino/gambling sites do you have in mind?
Playtin and Just-Dice for now.
another scam, don't bother wasting your coins on this crap
That's your opinion.

So, why can't I just invest in Just-Dice myself?
Some people may not have the time to deposit and invest into Just-Dice and would rather have another party do it for them.

I am more aiming towards Playtin shares however, I believe they are a good value considering their dividends.
There are people out there so lazy that they can't send some BTC to a site and click 4 buttons? Damn, I can only imagine the struggle when they get hungry..