Even if some people just like to be a miner and not benefiting from it, it is still not a hobby for such person because no pleasure derived from not benefiting from being a miner.
I think many people see mining more as a work because of its costs. One would think ‘why do this as a hobby when it is so costly and expensive to do? Why not get some profit from it?’. But maybe some people do not necessarily need the profit from mining and they just genuinely enjoy doing it. Just because we don’t and won’t find it pleasurable doesn’t mean it’s not pleasurable for others.
The pleasure I mean is the one that makes your hobbies to be recreational activities that can even benefits your health like riding a bicycle with friends, reading story books and novels, watching movies and sport events on TV et cetera.
The definition of hobby is any activity that is done outside of work hours and gives enjoyment to the person doing it. It could literally be anything and not just restricted to the examples given.