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This is just basing up with my own view on why theres no platforms adopt it.
1. Less demand/interest
2. Boring to look at (Less physical movement etc)
3. Time consuming
So its not surprising that platforms would simply just ignore this one.
A huge respect to your point of view in my suggestion. Yet as what @livingfree already have said, only true players and fans knows the worth and enjoyment chess regardless on what medium it is broadcasted with. Let me breakdown the stereotypes, explain what made those exist, and what really does happen in a mindset of a chess player.
1. Less demand/interest
It is true that most of the physical-adopted games tends to have more demand and interest such as basketball or boxing. But with the chess masters streaming chess games and even making their own tournaments on twitch
(Hikaru Nakamura and Botez Sisters), chess somewhat became a common game to stream on
(look at Twitch - have 2M followers on any chess gamers), even xQC and Moist were addicted to winning it against other streamers. Hence, there are demands, just not on the betting market.. yet.
2. Boring to look at (Less physical movement etc)
Well, some really are bored watching people play chess. SOME, but never ALL. Some people even unknowledgeable in chess tends to enjoy it. How do I know? I even watch MINECRAFT streamers stream Chess and their watchers still maintain to be 5K upto 70k+. How was those viewers still watch those if it was boring? Maybe it wasn't. Or in fact, it really wasn't.
Should I still explain why it isn't time consuming? Apparently, chess games and streams are even more watched than other games, how? It really just depends on the players and CASTERS. Casting is such a huge thing in online tournaments. We just really aren't that familiar those exists.
Lastly, it really is surprising to the fact that those things I say is true and exists. Maybe the betting market has standards or maybe they are just waiting for Chess to be a real mainstream game online? We don't know, until it happens.