It's not a problem of players or the devs saying there isn't a solution, it's the practicality of of developing it for a game that comes out with such regular content updates. Resources and time are finite and from a development standpoint there is little logic in developing an entirely new system as well as increasing the workload of the asset team, itemization team, etc. When a simpler solution is on hand by simply creating jobs that continue to share the existing gear.
It's a matter of choosing the path of least resistance which is absolutely necessary in developing this game.
Later Edit, rather than make another post:
This is exactly the problem when people start talking how things would be so easy, they show they have no idea what they're on about. You are aware that Int gear already has Vitality on it, right? And that converting all the Int into Vitality would mean that tank has more HP than the others by quite a bit, on top of that, they now have no primary DPS stat to go off of.
There are plenty of reasons a tank cannot easily use Intelligence gear, many of which I've already listed.
It's complicated in the sense of itemization, and on the end users (the players), having to consider equipment that has different stats depending on which job is wearing it. It creates a massive gearing issue between the jobs sharing it, you're still in essence creating 2 different pieces of equipment except with the added development of creating a system to easily display these stats. It still doesn't broach the idea of how it's generally a bad idea for different roles to have to compete with each other for loot. Part of a perk of playing a tank or healer is just that, knowing in most content you are relatively uncontested for drops. This works as a positive incentive for players to play tanks/healers, and taking that away is a step backwards towards getting more people to play the role(s).
Please do point out where I ever said it was impossible, because I absolutely never did.but this too is in a few too many MMOs to call "impossible"