This ban was long coming, if the streamers presented gambling in a responsible manner and they were honest about what you could expect out of gambling then I do not think they would have done something like this.
But this is not what happened, streamers began abusing their position and those watching them enabled them, so Twitch has decided to finally take action against them, and while this is a step on the wrong direction when it comes to the popularity of cryptocurrency casinos, I think they did not gave Twitch any other choice.
If I remember correctly, there was already a similar scandal regarding sexualized content and Twitch also took action, but little (if anything) has changed since then. The most popular streamers both did streams in pools and continue to do so, as they licked microphones and continue to do so. In addition, in the channel description they have links to their OF profiles or even to porn sites where they earn the main money. Maybe these restrictions regarding gambling are also exaggerated and will not affect anything?
While it is true that there will always be people trying to abuse the platform and violate their regulations, at least if they prohibit it on their TOS this means that as soon as someone reports those accounts and someone follows on that report then a ban can be issued without having to give any explanation to the offending account, as they knew what they we are doing.
So while this is not going to stop people from creating that content and using Twitch to promote it, at least we should see a reduction on that content appearing on their platform.