RP codes being region locked

Okay, I have redeemed over $400 worth of RP on my NA account over the past year. Now I am getting errors saying the codes are region locked. Why? Like, Riot still gets their money, why does it matter where the codes are purchased? I don't want to play on the Oceanic server for a reason. I don't want to spend my money on a card I can't even use on my main account. I realised this has only been happening recently. Like I said before, why does Riot care where the codes are purchased, they still get their money