The Pico/RP2040/RP2350 ecosystem is more competitive because it's a distance-to-the-metal thing.
At this point, most "mainstream" Pis are being used with off-the-shelf software or at least an off-the-shelf OS with custom userland code, and the technical details of the Pi are black-boxed away. So any competitor just needs to get you to the same basic "here's a Linux distro with the common packages" to get to a basic product parity, and then can differentiate with more/better/cheaper. This is especially easy when you can target a vertical specifically, like the "router boards" that come with an OpenWRT package.
The Picos are being programmed at a low level. If you want to swap in a STM32 or CH32V, you're a lot more concerned about "are the reference docs available and accurate", "will there be a reference to my specific weirdnesses on Stack Overflow", and "do the dev tools actually work." From that perspective, the RP products are industry leading, at least to a "Nobody ever got fired for buying ~IBM~ RP2040" level.
STM32 would be the IBM of the embedded world, but that doesn't invalidate your point; RP MCU's are documented well enough and stable enough for professional work.
At this point, most "mainstream" Pis are being used with off-the-shelf software or at least an off-the-shelf OS with custom userland code, and the technical details of the Pi are black-boxed away. So any competitor just needs to get you to the same basic "here's a Linux distro with the common packages" to get to a basic product parity, and then can differentiate with more/better/cheaper. This is especially easy when you can target a vertical specifically, like the "router boards" that come with an OpenWRT package.
The Picos are being programmed at a low level. If you want to swap in a STM32 or CH32V, you're a lot more concerned about "are the reference docs available and accurate", "will there be a reference to my specific weirdnesses on Stack Overflow", and "do the dev tools actually work." From that perspective, the RP products are industry leading, at least to a "Nobody ever got fired for buying ~IBM~ RP2040" level.