Mining is not what that should be regarded as a hobby. Or I can not consider it as a hobby. The reason for this is because I do not think someone will say he is mining bitcoin for pleasure. Hobbies are activities that you do for pleasure.
I think that there are people who consider mining a hobby. In as much as we know that there are a lot of cost involved in setting up a mining rig even if it is a small one, there a people who by virtue of their geographical location and other factors are already at an advantage that enables to afford to mine as a hobby. For example people who live in areas where the cost of electricity or energy is lower than in other places. In addition, people who live in areas where mining equipment like the ASICs are cheaper that in other areas.