OP no one is stopping you from armoring all the jobs. And your complaint is not valid, because your rant is about the sealing every game has, not what you are allowed or not allowed to do.
FFXI: 6 months in sky for a pair of pants, 1 year in sea for one necklace, 3 months camping for a pair of gloves..... salvage for 2 years for one body.
WoW: one full years before one a weapon i needed ever dropped, and 6 people looted on it!

I know they seem the same, but are not. Not allowing you would mean that once you get 1 body for 1 job, you can no longer obtain any other body armor for other jobs. Sealing caps weekly progress so people do not rush and burn out.