I'm arguing that due to networking effects, having decades of tribal knowledge is worth the cost to keep it. Starting anew elsewhere, even with smart people can sometimes take decades to build that knowledge.

Look at SF, every company competes in that market for software engineers because that's where the talent is.

It's actually a concept explored by the book "The Talent Code", and even explains why so many people from puerto rico (by population) are so amazing at baseball. Everyone plays, everyone looks up to it, and everyone makes everyone else better.