For me, there are many aspects involved. One thing is for sure that bowling can be played "on your own" and in a team, and I enjoy both very much.
When I practice, I like to challenge myself, or just enjoy the "feeling" when I read the lane correctly, make proper adjustments, and either improve carry or stay "on line". It's the same when the lights are on in tournament or league.
Additionally, I like the maynfold aspects of the game, and how they work together. There's the physical aspect of proper execution, but also the mental game and the technical side to the sport. You have to combine these things in order to be a "good" player. I do not claim to be one (far from it), but understanding how things work together and learning how and where to turn the knobs is a big part of bowling's fascination for me.