Ummm...
1) Why would you need a reason?
Seriously, there are Farmers in Mainland China whose hobby are
constructing movable robots. And one of the worst movie directors in our generation who
beat the crap out of his critics in a boxing match. And of course there're waaaaaay more other examples out there than those.
They wouldn't make any sense by your definition, but there they are.
2) So if you feel you really need a reason,
come up with one.
It's a TRPG game where your characters are all from imaginations. If you need a reason, just imagine it.
It doesn't even have to make sense (like people in martial arts movies doing backflips or fighting over a dozen people and winning-level of don't make sense; Or in TRPGs, saying "Cthulhu Exist"-level of don't make sense.)
In the world of imagination, as long as you don't say it doesn't, it WILL make sense. Tl:dr, Relax, and use your imagination.
But well, the central reason is just: CoC is a skille-based game, and many of those jobs just don't have that many skills that're game-related or gameworthy. Customers are going to complain if they don't at least get a vague feeling of balance, so designers have to literally squeeze skills into places even if it doesn't make a lick of sense at all.
This ain't just a CoC thing.
