Just because it's in your library from an Origin-era purchase does not mean it's still available for purchase now. In fact, a good chunk of old games were delisted as they're not fully transferred to the EA App.
Topic on User talk:Patrxgt
It's not in my library. I can buy Populous: The Beginning for 14,99 PLN.
From where, not counting GOG?
EA App. There is also possibility to do this on EA's website, but it's a little buggy and doesn't show correct price. If you ask me, it looks like regional lock (even if there is no reason for such).
Odd, I just switched my region from Croatia to Poland and even Ireland, it doesn't seem to show.
Strange indeed. Maybe try some VPN and using different browser, so you have fresh cache and no cookies, that could trace EA to the country you live in.