Puzzles are simple when it comes to rules. Match colors, draw a line etc. That means it doesn't  require a lot of though or concentration like "deeper" games with stories and such. Puzzles also don't require a lot of time so if you need to quit rapidly you can do so. I see more and more people playing puzzle games all the time. People sitting some where waiting for end up playing bejelwed on their phone. Quick and easy is my motto.