[Autumn]

The short answer is:

Everyone is playing rock-paper-scissor in mechanical combat.

At some point, scissor got tired of losing to rock, so it picked the best choices available to it, equipping the best gear, and the best combat style of the given time period, and thus became an atomic pair of scissors.

Then people saw how well those atomic scissors were doing, and copied it.

It was never that we didn't have options, it was that the atomic pair of scissors were too good not to run.

Even though I agree with this pretty heavily at some points (See: The abundance of VAs popping up recently due to mage meta)

I do think opening up diversity is a good option as well, though as you say, the best options will always be the flavor of the month. That much is unchangable no matter what kind of overhaul you throw at the game. Its always easier to notice them above all other options too, even though there's a quote unquote "Mage Meta", only about 25% of the active character base are realistically mages, and the rest are Black Knights and/or duelists. Its just easier to notice the VAs and the Mages up at the top of the rung at the moment.