The exec in question received an offer from one of the Big 4 at an equivalent (and possibly more senior - this was in late 2017, so memory is fuzzy) exec-level position, and simply sent word they wouldn't come into the office the next day. There was no two-week notice or polite exit interview - they just vanished.
It was not common news that Tracy was pregnant at the time, so I do not believe it factored into his decision at all.
The exec in question is very well-known and had lead successful teams at much bigger companies before. We speculated, at the time, that he had found working for a startup to be a very different beast instead.
So Big 5, really, but I feel Apple is usually omitted because its primary focus is consumer hardware and the software is usually an ancillary product.
But here are 2 things to keep in mind:
1) Founders, and some engineers, join a startup for the vision or adventure.
But most other staff, especially salespersons and executives, are there for reliable cash. Not "on-the-come" or "we'll see where this goes."
I've interviewed salesmen for a startup, and the first question they ask is, "What's the base salary?" And it better be risk-free and close to $100k in SF, regardless of the commission. Or they'll just think, "Time to call my buddy at FAANG or Oracle" and walk out.
2) If you haven't had a child, then you don't know what the dramatic physical, mental and social impacts are. The author described mostly the physical side of having a child, but not the other 2 factors. Post-partum depression can have long-lasting effects far beyond the act of giving birth - my partner behaved literally like a stranger for 18 months. What you see on TV is definitely not reality.
I was a bit confused, did the tech exec just quit without notice when they learned the CEO was pregnant? How would they be able to justify that insanity to their next employer?