speaking from personal experience, it's not that good to have TLM as your manager because in some ways you're competing with your manager on technical scope, and you'll lose
Once you're late stage though, that's done. TLMs are probably being held to 100% of IC standards and manager standards, people under them are jockeying for "impact" and don't want to compete with their manager, etc.
I totally see why it wouldn't work at today's Google. Honestly maybe it's a positive sign they recognized that.