PIO can be PWM, SPI, I2C, USB, DVI, VGA, ISA-bus, PS1 memory card, that weird protocol some old EL-display uses and hundreds of other peripherals. Lots of exotic protocols for which you would have previously needed an FPGA.
Or I would just choose an NXP IMRXT-series MCU with FlexIO (which can do 90% of these protocols) and actually be able to protect my product to some degree (encrypted XIP, high-assurance boot, SWD lockout.)
As well as better ADC, "halved" (half mem, IO, PIO and CPU) cheaper version, "doubled" version (2x mem, IO, PIO and M4f CPU cores), integrated flash version, etc. Better power consumption.
That said, I do like PIO and you can use RP2040 as a PIO-peripheral to something more protected.
That's why you'd choose RP2040.