There's really only so many ways to create all/many job equipment that is useful to more than a few of them. And if you include stuff that's very job specific (i.e. pet bonuses) that takes away from the power budget of the item while not benefitting any of the jobs that don't have pets (for example). This leads to all jobs gear just being really generic and only having common stats like accuracy/attack/MAB and main attribute bonuses.

So as nice as it would be to have gear like this that could potentially ease up item storage frustration (by having stuff that's useful to many jobs to free up slots), from a functional/utility standpoint, this isn't as great as it sounds on paper.