PSRAM with 32-bit data bit depth
Increasing the number of data bits requires an increase in the number of pins or bumps on the package, which increases the physical size and cost of the package. Note that PSRAMs typically do not multiplex the address pins as DRAMs do.

So, the 32-bit version is a more expensive product that takes more board space and has a smaller market than the combined market for 16-bit and 32-bit PSRAMs. The economic incentive is for the PSRAM manufacturer to sell a 16-bit version, and let those who need a 32-bit data bus combine two ICs at the board level.