There is just an insane amount of engineering and work you have to do. Measuring text and shaping fonts is a nightmare, computing chart atlases, having infinite scroll with virtual lines coming to and out of the screen, all the strange data structures to preserve optimized decoration rendering, ropes and ropes (hard data structures), navigating with the keyboard, computing which character interaction is closer to the I-beam when jumping up and down, also caching your previous movements to go back where you actually were. CRDT and atomic editing strategies... There are hundreds and thousands of articles and papers and stuff covering these things. It’s just something we take for granted with so much beauty in the background.