But assuming that NVMe and SATA SSD controllers emit the same energy, it makes more sense that NVMe would be hotter.
Think about it. If you throw a ball of high heat meat would it cool faster if it was connected to a large body of water (SSD with its chasis) or a small body of water (NVMe small piece of plastic that is the NVMe)?
Another thing to check if your NVMe either has proper thermal pads placement and/or if the air from the front coolers is reaching it.
Which is ironic because NVMe was supposed to be more efficient and doing less work because it's design wasn't bound with SATA&spinning assumptions and controller doesn't need to handle pcie-SATA conversions since it's directly connected to the bus etc.
There's also the location of the temperature probe, it doesn't need to be much further away from the heat source to register drastically lower temperatures in either case.
One problem with m.2 is the spec would permit a module with the controller on the bottom where it would be difficult to cool. But I think so far nobody has been dumb enough to ship one.