Gypsy (that first modeless editor) recently turned 50 years old and I wrote about it here largely from those first-hand accounts: https://digitalseams.com/blog/the-gypsy-document-editor-cele...

And it's not mentioned in this ACM interview but rather this one with the Computer History Museum https://archive.computerhistory.org/resources/access/text/20... that implementing a modeless editor was easier too, since you could use a simple case-switch instead of having a bunch of explicit modules for each mode.

I have come to modal editors after decades of modeless, I enjoy them - but respect, understand, and appreciate Tesler's efforts, and I always enjoy reading about them.

So much of what the Mac was came from what Tesler built into the Lisa project based on his personal convictions on what computing could be.

Jobs got a reputation for "taste" but a lot of the origins of what that looked like in practice were Tesler (and others, obviously) driven.