There's a good podcast called Acquired. Highly recommend it. They're private equity guys who cover the history of companies and what made them great, and cover the topic very well.
For IBM and AT&T, from what I gather it seems like they missed out on multiple waves of new technologies because there wasn't a market for it, or the revenue was so low it wasn't worth their time. They were market maintainers, not makers. They also rested on the fact that they were the incumbents, so made the incorrect assumption that people would always default to them out of convenience.
Your second question basically falls back to whether FAANG make the same mistake; resting on their laurels while some small fry breaks into a market they deemed too small to serve.
I really liked their recent one on Microsoft. They cover how intertwined Microsoft was in the early days with IBM. IBM did notice the trend towards PCs and made it a skunkwork project out of Florida to remove it from the IBM bureaucracy.
Second there is a book called “The Difference between Larry Ellison and God” which was about the early days of Oracle. Oracle’s SQL database was built entirely on research from IBM and a bit from Berkeley. IBM was slow to commercialize on SQL but the reason SQL is a standard is because of IBM.
But one of the interesting things that the podcast covers is that IBM was so large and powerful they were stymied to make the big moves necessary because it would have led to antitrust action. So even though we think of it as ineptitude there was a reason that they missed the mark.
For IBM and AT&T, from what I gather it seems like they missed out on multiple waves of new technologies because there wasn't a market for it, or the revenue was so low it wasn't worth their time. They were market maintainers, not makers. They also rested on the fact that they were the incumbents, so made the incorrect assumption that people would always default to them out of convenience.
Your second question basically falls back to whether FAANG make the same mistake; resting on their laurels while some small fry breaks into a market they deemed too small to serve.