It's because they're considered "Off Duty" and only Feds have that class of clothing.
It's stupid says I.
All factions now have access to off-duty clothing (since the summer event). Perhaps the devs just haven't gotten around to altering the permissions on the ferengi clothing packs. The other options are that there's a specific part of the costume that doesn't work with KDF models (and would require extra work), or that since KDF has lobi skirts, the jackets must be fed-exclusive forever, but I would tend to doubt that one.