It's pretty much an RPG tradition that you can only rare too rings and one amulet at any given time, and probably goes all the way back to D&D, in any case, I at least can't name a game I've played that let's the player wear more than two rings. Usually, the reasons sited for this are balance, though I'd argue that just adjusting the numbers could address that. Still, as said, weakening enchantments to allow multiple rings to not be unbalancing would probably not be appreciated by fans, in the end, developers probably just figure they'd rather stick to the setup that has always worked before.
I don't think the ability to wear more than two rings should have any effect on enchantment balance issues. You still only receive the benefits of one enchantment per hand because your body is only able to absorb a single enchantment in any given area.
Seems like kind of a flimsy handwave to me, not to mention it renders wearing multiple rings pointless from a gameplay perspective, why wear more than two if it doesn't do anything? And how would the game decide which of the equipped rings to use enchantments from?