Thirty years ago, Dave Smith worked with Roland on a way to make synths and musical instruments communicate. They connected a JP-6 and a Prophet600, and MIDI was born.
Since then, it has been (and still is) at the heart of musical hardware, and even though the technology is behind other means of communications (Bluetooth, WiFi), its presence is still expected. What makes its strength is its simplicity: not much hardware is required, the messages are simple enough to be handled by a small microcontroller (or even discrete logic chips, with a bit of courage), and since it’s not in constant change, there is no need for updates or revisions.
The first MIDI device I made was actually not a musical device. It was an accelerometer-base inclination meter, made for a school project, and we figured out it was a convenient way of transmitting data between the board and the computer, since there was already a program on the other side that can understand the data. Then I started controlling MIDI effects, like the Digitech Whammy, from an Arduino, and that’s when I started developing the MIDI library.