I’m having a hard time finding a reason for this. Especially since NONE of the benefits apply. I’ve seen people cite HP but that seems to not be true. I’ve got a Hearthling with close to level 30 and 5 in body. Who despite this only has about as much HP as a body 5 level 6 archer.
It just seems weird, since it means we’re basically being punished for having Hearthlings switch professions or even “rank up” for absolutely no good reason?
It’s to discourage “jack of all trades”/“super hearthlings” trained in all jobs; as a rather blunt and inelegant way of encouraging players to spread the jobs around between different hearthlings. The ultimate goal was to promote interaction with the different hearthlings, but I think it falls short there since it just makes the creation of those super-hearthlings more tedious; it doesn’t give any advantage to having complimentary skill-sets on different hearthlings.
Seems weird, since they can only do one job efficiently anyway. Which means a single hearthling trained per job usually works out better anyway.