It says "VMC Only" vice "VFR Only" because you can execute a circling approach at the termination of an IAP after breaking out into the specified conditions...in the 121 world, all of that is normally done under an IFR flight plan, right?

If it said "VFR Only", you would have to break out into VFR conditions, cancel IFR, then proceed with a non-IFR visual approach...kind of ridiculous. Actually if you were to do all that, and then lose the field or end up IMC, ridiculous would be an understatement.

Remember VFR vs. VMC from private pilots days?