A hobby is a regular activity or interest that is undertaken for pleasure, typically done during one's leisure time. Thus the hobby-ist came into being i.e.  named that due to the participation in buying companionship as a regular undertaking of pleasure.

The phrase "hobbyist came into being in 1830, from hobby + -ist. Hobbyism is recorded from 1846.

late 13c., hobyn, "small horse, pony," later "mock horse used in the morris dance," and c.1550 "child's toy riding horse," which led to hobby-horse in a transferred sense of "favorite pastime or avocation," first recorded 1670s, shortened to hobby by 1816. The connecting notion being "activity that doesn't go anywhere." Probably originally a proper name for a horse (cf. dobbin), a dim. of Robert or Robin. The original hobbyhorse was a "Tourney Horse," a wooden or basketwork frame worn around the waist and held on with shoulder straps, with a fake tail and horse head attached, so the wearer appears to be riding a horse. These were part of church and civic celebrations at Midsummer and New Year's throughout England.

Now that I have you totally confused..