There are no other way on how to monetize your site and its really impossible to think of that a gambling site owner wouldn't think
on how he would profit and charitable works is quite not common nowadays even millionaires do create their own business online
to gain up something out of their funds and doesn't tend to give out free service to the community.We know that staffs and maintenances
do have some cost and running a site will really have some those expense and making no profit wont be sustainable.
they can run ads on thier site just like what other websites do , so that they can keep the site up and pay other maintenance cost . you mention charity ? i see some gambling sites are now giving some of their income on the charity that they choose based on thier poll . the title really says it all . this gambling site is really unique to have a zero house edge if ever the owner pushes it . this can get instant attention resulting for them to become indemand which can make thier site run longer than usual
No they aren't bothering theirselves on having that ads option as they say.

We don't want to bother our users with ads.
If this gambling site that do have true intent then congratulations but as a gambler or even just a person that do have common sense on how business works then
its hard to think that a service do offers no house edge thing unless if its temporal then its understandable but this one pertain or tending to be free or houseedgeless forever then
you cant blame people not to question out.