The last time (previously), and probably the last time (ever), that I flew Frontier, I didn't pay for seat selection. Although we booked together, they placed us 10 rows apart in the airplane. When we went to board (my partner is mobility challenged and gets early boarding), they found that she needed help boarding and, miraculously, found that the seat next to her was unoccupied, so they put me in it so I could help her board and a flight assistant wouldn't have to.
what would be the point in separating two people and causing needless ire for 0 gain?
Ask Frontier, 'cause that's what they did. I'm sure their "algorithm" did that deliberately so that the next time I would pay the extra to sit together. But there probably won't be a "next time" with Frontier.
If, for weight distribution, they spread the empty seats out evenly, almost everyone on the plane today would have an empty seat next to them, without having to pay for one. I'm never going to fly Frontier again (unless it is the only option), but I wish someone would try this experiment. Book Frontier without paying the social distancing fee and see if you are one of the only people on the half empty plane sitting next to a stranger.