I'm not sure if I count, but I suspect two things. Heat dissipation and controller complexity. NVMe controller might be more computationally heavy and so they m

I'm not sure if I count, but I suspect two things. Heat dissipation and controller complexity. NVMe controller might be more computationally heavy and so they might emit more heat*. 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.