Odd... I feel, like wizards, a few classes could lean on a trinket-like item. Certainly not all need to. I think having partially fulfilled layers of classes that differ is what makes things interesting in class based systems.
I don't see it as that odd. Grimoires were central to the Wizard class from day 1, providing a significant portion of the class's power and flavor. The other classes (so far) aren't structured around an item like that. What class functions do you take away and ensconce instead in an item? And, if you do make the trinkets that powerful across-the-board, then you have the problem of ensuring that each class (and, in some cases, each flavor of each class) has access to appropriately leveled trinkets throughout the game.
If, on the other hand, you make the effects of non-grimoire trinkets comparably small, well, why bother with all that extra work? If it's just another equipment slot that you can fill with a +5 Deflection item (or whatever), well, you can get similar class-flavor effects just by having some exclusive hats or belts (soulbound or otherwise).
It would've been nice and neat to have the classes all have parallel equipment slots, but I get why they decided that this was a lower-priority feature.
My understanding is that equipment slots are restricted to specific bonuses now, so a trinket slot could be more flexible and generic.