Hmm, that's odd, unless maybe you signed up for the public beta program in the past, and maybe it's using that.
It's based on your Apple ID, not your device, and as far as I can tell, Apple still wants people to sign up so they know what they're getting into.
Are you seeing both the public and developer beta options or just the public one?
I tested multiple scenarios on a few different iPhones and iPads while I was doing
an article on it. In my case, it didn't appear until I signed up (again) for the public beta software program. Before that, I only had the iOS 16 and iOS 17 developer beta options showing up with my primary Apple ID, as I'm a paid member of the developer program.
I also tested it using several other Apple IDs. One of which had participated in the iOS 16 public beta last year, while two others hadn't ever been used with any beta programs (one was years old, while the other was a brand new Apple ID I had set up specifically to test this). The iPhone that had previously been on the iOS 16 beta program showed only the option to get iOS 16 Public Betas, while the "Beta Updates" line didn't even appear on the rest.
That's also the case for all of my family members' devices, except for my daughter, who opted into the iOS 16 public beta last year. As a result, she's running iOS 16.6, but she isn't seeing any options for iOS 17 as she hasn't signed up for that.
This was also on iOS 16.5. I do recall the beta update setting's behavior being a bit flakier on iOS 16.4 when it first came along, so it's possible it may be different there. I didn't have an iPhone still running iOS 16.4 that I could test with.
However, this also changes once you've installed an iOS 17 beta, where the options will appear regardless of whether your Apple ID has opted in or not. I suppose that makes sense since you would need to have opted in to get the iOS 17 beta in the first place, and folks who are testing with different Apple IDs might miss an update if they switch to one that's not a part of either program. That same logic also applies to iOS 16 beta point releases like iOS 16.6.