just speculation on my part (and an opinion, I don't know about you, but even if someone says it's safe to eat irradiated food, I would strongly prefer not to eat it)

I would imagine is difficult to avoid irradiating other things while in the process of irradiating food, also NIMBY probably? I don't think the FDA is trustworthy enough for everyone, so even if they say that it's safe, I think many people would prefer non-irradiated food, to the point of it not being worth it for companies to irradiate it