I used to think the same, I have had some casinos I played at where I never managed to win enough to withdraw and I done a lot of deposits at them. Stan James casino which has now been merged with
Unibet. That casino I think I withdrew like twice in over a year of playing their. There was a few casinos where I never withdrew from. Vera And Johns was another where I found it extremely difficult to win at.
But at the end of the day all casinos are doing is hosting the slots from providers. They pay for licenses from providers to host their slots in their casino brands, all casinos can do is if a provider has various RTP options for their slots then a casino can decide to pick lower RTP versions of the slots. This is now becoming common as a lot of casinos are now starting to pick lower RTP versions of slots and they blame it on higher tax levels etc etc.
But I think it is just random. When your in a lucky streak you can keep winning at multiple casinos the same day or during a week and get withdraws at every casino you play at in a short period of time.
Also one final point. Some casinos I play at now have some providers and slots other casinos do not have. So when I do play at the other casinos now it is because I want to play a specific slot that no other casino have available for me. Like for example Partycasino has Euphoria from Isoftbet and Katmandu Gold from Elk and some others too, So I find me wanting to play those slots only at those and I ignore all others. At Videoslots casino which is my main casino. Since they reduced the RTP in a lot of their providers, Pragmatic, Red Tiger, Net Ent, Play N Go, a few others. I now play these providers at Pokerstars when I want to play their slots.
I am doing well at pokerstars in terms of my deposit and withdraw ratio. I think I am now close to even since the last time I checked. VS is a different matter, More deposits than withdraws over the last 5 years lol.
So the casinos I play at now are these:
Videoslots casino
Pokerstars Casino
Party Casino
Grosvenor Casino
Ladbrokes Casino
It is funny because when I asked live chat in party casino and ladbrokes if they are linked or owned by the same group they denied it. But when you look at their websites they have the same Design when you open slots. I then did some google searches and I found their parent company and they list both of those brands in that parent company - Entain plc.
So clearly live chat were clueless
Also for a very very long time I found it impossible to win at ladbrokes. But now I win and withdraw often. I went a year once at ladbrokes where I never won enough to withdraw. Then I had periods where I kept winning and done loads of withdraws etc etc. It is just random.