[osy]

STM32H7 is just an example. Most (all?) STM32 with has hardware SPI slave support. For example the STM32F030C8T6 is on JLCPCB as a basic part (no per-part cost for assembly) at $0.82 while the RP2040 is $1.11.

While the RP2040 and RP2350 has a much nicer to use SDK and for certain applications like USB it is much easier to set up, the STM32 is much more versatile and is just a much more mature product (don't get me started about the RP2350 having broken pull-downs on GPIO pins).