Verdeva, hit on it I think.
Yor feeling the "parasitic friction" of the wet clutch. Because it is in the oil sump, and there is friction, or a restriction to the free movement of the clutch plates, from the OIL, the clutch never fully disengages. Kinda, in a way, acts like the torque converter in your cars auto trans. Cold or thicker oil will grab the plates more than light or warm oil.
93 VT1100C Sleeper, VH Exhaust, Saddleman Seat, Baby Apes, Metzlers, 2mm sleeved and bored (1150cc),10.5:1 comp, Modified Heads, Valves, Cams, Adjustable Timing, Bored Carbs.