And a lot of smaller microcontrollers still use a UART port and serial protocol to reflash the device. It's the lowest common denominator for hardware interface and the simplest thing that works.
Hah, to me flashing an MCU over UART is a luxury. When I first started working with MCUs I needed to use a chip programmer that cost several hundred $ and flashed using a high-voltage (relatively speaking) parallel interface. Then there were serial programmers that used a proprietary protocol to talk to the chip. And then finally we had bootloaders and self-flashing MCUs that made this whole process sane and affordable!
And of course to our ancestors, we're spoiled kids with our electronically erasable ROM ;)
I remember being blown away as a modern teen seeing an old EPROM being erased and how to do it. It felt more hacker like than todays "just push a button"
And of course to our ancestors, we're spoiled kids with our electronically erasable ROM ;)