I don't think anything here is inherently wrong. I like when my partner sends me nudes but I guess it's not for everyone. Maybe he genuinely doesn't mind the OF, but isn't particularly interested in it. That's legit. What is concerning to me is that it seems that you're not getting the feedback from him that you need to feel attractive and desired, and that probably is something that needs to be addressed if you want to maintain a healthy partnership.

If you decide to address it, I wouldn't frame it as "why aren't you interested in my nudes/my OF?" Instead, I'd frame it as "I'm feeling like you're not as attracted to me or as interested in me as you used to be, I want to feel desired by you, so let's work together to find something sexy that we both enjoy."