There has been a tendency among the Southern states (AL, GA, SC, NC) to avoid duplicating x85's across the states. If you look back at the "sequence" of number issuances over time, it sort of goes like this:
GA (planned, never built)
185 GA (first duplication)
485 NC (Charlotte loop, number never signed in GA)
785 NC (planned US 29 upgrade)
285 NC (planned US 52 upgrade)
685 AL (unsigned on temporary I-85 through Montgomery)
So, 885 has never been used in a state so far. I think that's part of it.
Otherwise, why did they choose I-785 years ago? To not repeat SC's
185/385/585, or GA's 985.
I-885? that is going to be interesting. Why don't they use I-685? (I-285, I-485 and I-785 are already taken).