I think it’s just a proximity thing as they’re close but also not in the same conference. Last thing teams want to be doing is flying all over the country for an essentially meaningless final game of the preseason.
Any kind of joint practices are going to be great. I think that’s the way the NFL will head eventually, cutting back to two preseason games but with a couple weeks of joint practices sprinkled in to make up the difference.
That’s probably one part of how they’ll get to 18 games, along with some roster expansion so you don’t have to trim your team down to the bare 53-man team.