Why not?
If you are referring to the list, it states that “Devices can be added or removed from this list based on the status of the build.”
It’s hard to imagine FP6 not getting Android 16, because Fairphone have now released Android 16 for it and could help via the Fairphone - Murena partnership, and FP6 is actively being sold by Murena.
FP3 should be a big question mark for technical reasons (I read about kernel trouble), so FP3 users like me shouldn’t bank on it, but the end of security updates for the available Android 15 is to be expected in early 2028 if prior Android versions are any indication, so no reason to panic now.
Same goes for FP4 and FP5, which should be in a better position than FP3, of course.