A lot of it has to do with the government regulating people's actions. Its mostly artificial so I doubt that it will stay as a long-time trend. Things will slowly but surely go back to how they were, so online gambling casinos as well as physical casinos should see this as a short setback. I think they would have been better prepared if the governments gave a few months warning before implementing further restrictions and lockdowns. Most people had no idea what the government was going to do next and it really messed up people's businesses.
Outbreaks do not wait for anyone, so I don't think that giving casinos the leeway of waiting for a few months to get ready would help either sides anyway. More and more people would just contract the virus and more and more funds will be spent to healthcare, which may force the government to order lockdowns that are even longer compared to when they ordered everything a little earlier. That will hurt their profits even more IMO, and business owners don't usually like that.