So is, "Open-source is becoming the only way to develop (and, especially, maintain) complex software". This is hyperbole. Complex software has been developed and maintained for over half a century, in myriad ways.

Top talent has access to thousands of other well paying roles. You cannot treat them the same way companies treat regular employees (badly). If you give them pointless work, or work without career growth, they can up and leave in a heartbeat. If you try and bully them or pressure them to work long hours or place pointless restrictions (dress code, start times, vacation policy, etc) on them they will leave.

In technical fact, not impossible but, in fact, common. In spirit, you don't really employ top talent, in the sense that subordinating it wastes it. You sponsor it and become a beneficiary of it.

Better to say it's impossible to keep top talent around for more than a couple of years. Once they start to get bored they leave.