There's a million and one peripherals designed for that specific combination that don't work seamlessly with other boards (even within the "official" Arduino family)
I mean your complaint about the quality of the library code, it's perfectly fine that the code sucks if it lets people do 1 million and one things they couldn't otherwise.
Do you really think someone programming an Arduino for controlling their cosplay LEDs cares if the library they used is poorly written? As long as it works it works.
They were never going to read the datasheet for an MCU and start figuring out bit masks for pin initialization, so it's literally a case of something is better than nothing, and there's no reason to gatekeep the environment that lets them use embedded systems
There is an Arduino port to STM32 (Blue Pill in particular), for those whose idea of embedded programming involves a bunch of delay() statements scattered around the library code, making sure no other peripherals can be used while you’re polling for the next UART char..