I think there's another level to this, when you put a superconductor in contact with a metal there's a proximity effect that lowers the Tc of the superconductor

I think there's another level to this, when you put a superconductor in contact with a metal there's a proximity effect that lowers the Tc of the superconductor. If you're using a superconductor that has a 4K Tc then you cannot afford to have your superconductor be weakened by the proximity effect. So the insulation is to prevent the proximity effect from happening. Here, since you're using a much higher Tc material, if Tc is lowered by a few K you still have plenty of thermal budget, allowing you to take the hit from the proximity effect but be able to save on insulation.