Today everyone is a miner as there are no other reasonable ways to make good money.
But also because it is a very enjoyable way to earn that money, for many people (I know some hate it). Mining is one of the most well developed features of this game, in my opinion. I like to take equipment so that on each trip I can do at least three different types of mining (usually laser, sub-surface, and surface). This makes the activities varied and interesting (and getting those subsurface deposits out of fast spinning asteroids is definitely one I enjoy). While I like to mine efficiently, I'm never in any rush - I find it a really relaxing experience.