There was once a thread that discussed which devices was the most preferred
https://bitcointalk.org/index.php?topic=5330179.0, PC, Laptop, Phone or Tablet but that thread was already two years ago with the most choices being PCs and in my opinion PCs and Laptops both provide wider visibility than tablets or Mobile Phone.
Maybe now the trend has changed so that more will choose to play with mobile phones, but laptops are my main choice because the big screen makes it more comfortable when playing.
I think it's not just about the trends, but more about how we started to use phones more in our regular life, and that means everything else started to be in the phones to get some screen time. If people are spending hours and hours everyday on their phones checking instagram and tiktok, then it makes sense for casinos to have a good app or responsive website to get people to gamble there as well.
To ask them to put down their phone and open up their PC to play would be too much work, and not really comfortable neither because you could just open up a tv series on tv and whip out your phone and gamble there while half-watch the series at the same time.
Indeed, gamblers who kills time might prefer to use cellphone when gambling it gives them the comfort to do other things just like how you give your example, you can gamble while watching tv, though gambler got different preferences when using which device they wanted to use in playing their games and which platforms are giving that comfort when they are playing their favorite gambling games.
Gamblers will take the easy way or easy access to play as instant as it can be, whatever ways they prefer casino owners need to comply and adopt to bring them to the business.