Since we only have a sense of scale for all but the largest space stations and orbital facilities, Camalot Command, Gabriel, Lum, Boeing Megaplex.
They may not be so much of a niche unit. You aren't going to fly ASF's into Cammalot Command or Gabriel. Your going to send Battle Armor and Space Troops, I suspect the spaces are big enough for mechs but not big enough to fly down, except for the Yard slips proper.
Might make sense to have some mechs to support your BA and Space Troopers. I think Orbital Facilities are more common than fluff says. Maybe not many CMO26 sized facilities, but easily 1,2 and even 3 km Facilities. Spreading over dozens of levels, for many, many Square miles of Facility to secure, with mech sized spaces and 0g.