This is true because the poor are looking for every means to get out of poverty and they might see gambling as an escape route unknown to them that it will even make them more poorer. Someone that's already rich will only gamble for fun and will do that occasionally, but a poor man will continue chasing his losses with the hope of hitting it big.
The part when casino get a tag name mostly when negative seems wrong, let’s keep gambling aside and view this from a different angle.
I would like to use drug addiction because people get easily addicted with drugs, for example someone gets addicted to drugs and the next thing everyone starts blaming the drug peddler for selling drugs or blaming the person for earning profit from the business where as the dealer never forced anyone to buy, same goes for gambling also.
Now the case of the rich and poor narrative, the rich has a high advantage of balancing their funds after gambling or take good care of their system after drugs intake.
There’s always a difference between both, I know the poor might look more vulnerable because they actually need a win but, the fact remains no casino is responsible for irresponsible gambling although people who are vulnerable are likely to promote gambling activity reason why the casino make every possible means to keep the platform perfect meanwhile gambling is optional.