Guild Wars 2

I mean, there shouldn’t be any big technical reason it is limited at 12. When customers want to give you dollars, you don’t turn them away like that

Its probably for economic reasons, to stop players from mass-hoarding items.

Technical limitations to the game perhaps? Maybe if they increased the max amount of account bank slots you could buy from the gem shop it would horribly break the game and cause you to lose a lot, or all, of your hoarded junk?

They did add crafting profession slots to the gem shop a good while back, allowing you to have more than 2 crafting professions on a single character (the slots are account-wide unlocks). Then later increased it by 1 or 2 more max. So anything is possible.

It is a mix between technical and server space. You see banks need to grow in block. That said servers need to save the same space for max slots weather you have them or not.
So if everyone had max then most likely Anet would add more bank slots.