Pay for your inventory.

[Fyce]

-Snip-

They update all character information every 15 seconds "juste in case of a crash", in order to avoid rollbacks.
That's the only reason, and quite a silly one.

I would understand why you would need a backup every 15 seconds when releasing progression content (Savage Alex), but during "normal" play, a 15 seconds snapshot of the entire server seems overkill, just to avoid a very tiny misfortune of someone losing something in a 1-2mn timespan.

So, to avoid that, no more inventory space for everyone. Hooray.