It's not the cost barrier that prevents me from getting into mobile games. It's not the small screen or the laughable sound. It's not the lack of original or interesting titles, or the difficulty of finding any specific title. It's not even that my phone is so old that I can't be sure if the online functions will work at any given moment. And only to a limited extent is it that cell phones have a horrid input system, since any designer worth his salt can find a way to work around using buttons meant for data entry rather than game control (WASD, anyone?). And it certainly isn't that I usually have a dedicated gaming machine with me anyplace the urge to play might strike me.
The big problem for me is that it is on a telephone. It's the same reason I don't use cameras, or any sort of music-playing functions, or anything else that would have to be interrupted when a call comes in. I use my phone for communication, and I neither want to have to say to a person "Sorry I mised your very important call, I was busy with a game of Tele-quest," nor to have to restart that game of Tele-quest just because I get a frivolous message. Unfortunately, all the phones I've seen have behaved in one of those two ways - either ending the game when you answer your call, or making it difficult to answer in the middle of the game.
I feel like a crotchety old man objecting in that way, but it's the truth. Maybe they've fixed that with one of these newfangled telethingums you see superfluous ads for all over the place. I wouldn't know. My phone is old. When it breaks and I upgrade (I am content to do this because, in my mind, a phone is not a gadget but an appliance), I'll see if they've done anything with. And then I'll proceed to the more savvy excuses listed above.