The infection risk is primarily for her, but who cares? She’s allowing the cross-penetration and she should be aware of the risks, so it’s on her should she get a UTI. If she’s naive, that’s not his problem. More likely explanation is that she’s desperate for attention sexually and is probably willing to disregard caution in exchange for a couple orgasms. That is based on many encounters with BBWs over the years.
Big buttfuck sows are always just grateful to have a penis pushed in them and will take it in their mud pit even if it hurts like hell. And I take full advantage of that fact and jackhammer them relentlessly until their mud is packed in their colon as hard as clay.