If you check gaming market, you will find that mobile gaming market is bigger than PC gaming or Console gaming. If you check the top games, you will see that most games are either made for mobile devices or have mobile version. Why do you think mobile gaming is popular?
Everyone is on the go. You see people on buses, trains and even in planes playing games on their phones.
I pass the time when I’m commuting playing a game on my phone. See many people doing to the same. We used to read the paper.
I think it’s because a lot of people prefer to play games on their phone now instead of on the browser. It’s a more accessible now.