GrapheneOS has a feature under Security > USB Accessories that allows you to configure when USB accessories can be connected to the device. The options are to outright deny them, deny them when unlocked, or to accept them regardless (which I believe is the Stock OS behavior).
During boot time, this doesn't apply. If someone connects a USB accessory during boot, it'll register. The reason that is not relevant is because the threat model behind this feature has to do with protecting user data. When the phone is on (and has presumably been unlocked once, putting it in AFU AKA After First Unlock State), someone connecting a malicious USB accessory to the device can potentially exfiltrate said data.
During boot, the phone hasn't been unlocked once, so the phone is in BFU AKA Before First Unlock state. Therefore, the data is encrypted at rest, and therefore cannot be exfiltrated by such a malicious accessory.
As for what other projects are doing and what their motivations/though processes behind features they add are, I'd suggest talking to them; we can't speak for them, and would rather not.