This came about through an interesting linguistic turn of events: podiare originally meant “to step on” and then it came to mean, “to raise up” — like, to put on a podium. A podium is, after all, a raised platform that you step on!
Helping someone, in Spanish, is thus a form of lifting them up — literally. Or maybe, stepping on them?
This implies a question: what happened to the -d-? The p-y of apoyar maps to the p-d of podium, but how did the -d- turn into a -y-? The answer is that, apoyar entered Spanish, from podiare, via Italian — it first turned into appoggiare, the Italian for the same! So the -d- turned into a -g- which turned into a -y-.