But GPIO pins are everywhere


Microcontroller ports are only part of the game
You have GPIO extenders over I2C
Most peripheral chips offer some GPIO pin
You can have a remote controller, behind pci/usb/whatever

We need a flexible API that can be extended over time
Really, you are expected to think about it, and we may see it later

Vendors solutions are not "usually" up to the task
They only offer register names
"IOSET1 = n"
Or they offer structures
"GPIOC->IDR"
I'm ready to apologize if you show me good vendor code

The Linux approach grew too complex over time
If features dynamic allocation of GPIO numbers: it can't work with microcontrollers