Doing something for a hobby sounds like doing that thing more casually. But many hobbyist are the most enthusiastic people I know and take their hobbies very seriously. There is a thin line between those serious hobbyist and professionals who do similar things. Sometimes the hobbyist can even outperform the professionals. The only difference is that the later group does it (mostly) for the money.
Turning a hobby into a profession is a risky move. As long as you are doing something just for your own enjoyment there is the freedom of doing as much as you want. But earning your living can bring an unwanted stress when your living depends on it. It can also restrict you when you need to do something that sells, something that somebody is willing to pay for. You can't freely choose your direction and be truly creative.
Of course it's nice to make some extra money on the side from the things you enjoy. Hobbies can still provide that without you having to give up your freedom or having to stress too much about making a living. But often it's the other way around. You need your day job to pay for the hobby.