A big consideration for efficiency and TCO calculations is the number of servers required to house the drives. NVMe drives tend not to be in external JBOF enclosures.
Fewer servers means fewer cpus, less RAM, fewer fans, and maybe fewer switches.
With a modern CPUs hitting 400W it's already a problem to fill a rack top down with servers like you could do before: too many heat to dissipate and transfer, too much power to provide in the first place.
Just imagine something like 2S 9565 in at least 2U machines: with 10 server x 2U x 2 CPU you would have 8kW in the processors alone and you didn't even fill half of the 42U rack.
Getting rid of 30 watts of heat is trivial compared to say, 300 (I don't quite know how to read that ratio since a 2.5kW SSD seems a little high to me).
