Personally, I don't get why Twitter is still popular and that a lot of casino really use it. It is full with bots and I really doubt if it is really so effective for marketing.
There are bots but at the same time real community as well so most of the promotions are done there.Moreover you will find the gambling community is active there while most of the other social platforms are not good and suitable for such promotions.They are getting attention from Twitter so it's going good for them.