According to the wiki page on flash memory, flash chips have built-in charge pumps to step up the 1.8v supply to a higher voltage to program/erase the cells. This wastes a lot of power and is apprarently a common failure mode. The wiki page mentions the idea of using a single shared boost converter for chips with a separate Vpp pin, but apparently this is not very common anymore. Besides, this still seems like only a half-solution; I recall reading that this voltage is on the order of 5-10 volts, a voltage range that is abundantly available on PCs.
For SATA SSDs, one could use the 12V rail if available, and fall back to a boost converter drawing power from the 5V rail; for standard PCI-e cards, there's a guaranteed 12V supply available. (m.2 appears to only have a 3.3v supply, which begs the question of why, given what appear to be obvious advantages of higher voltage supplies for flash)
I understand single power supply is convenient, but surely a couple more layers would be worth it for the efficiency and performance(?) benefits. And economies of scale doesn't seem like a good explanation, given there is a pretty large market for high-performance flash.
So, why are single-power-supply flash chips so ubiquitous?