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$300 Vision Pro developer strap is just an expensive USB2 device
(appleinsider.com)
This is a most excellent place for technology news and articles.
USB 3 wasn't an option whilst they were sticking with lightning, and if the EU hadn't forced them they clearly wouldn't have switched.
The reason the new non-pro iPhones use USB 2 is because they still use the old chip which previously used lightning, and as such never had a reason to support USB 3.
So I would say this is about the connector, even though you're technically correct that the protocol is separate from the standard.