TBH, I think there is more to listing than paying a fee. If I think about it, suppose there is a non gambling token out there with the same performance, popularity and from a pretty successful business, I'd say it would have been listed in a tier 1 CEX by now. I would say it's likely that there could be some friction with tier 1 CEX and gamba platforms in general.
Usually listing on centralized exchanges requires expensive listing fee and if you don't choose good exchanges with good trading volume generally, your listing fee can be spent for nothing. Your trading pair will be very in active and has very low trading volume if your token is listed on a small exchange.
If Rollbit want to list RLB token on more centralized exchanges, they will be very carefully in selection process on their next targets. They shown good dedication to build up the business, and continue development as well as support on RLB token but next steps must be assessed very thoroughly in cost and benefit.