> but confusingly adopted it as yet another excuse to generally rewrite the apple pie from scratch instead of just renaming things that aren't broken.

I think that inverts history. The YT Music implementation and brand existed long before the decision to replace GPM with it. The branding decision followed most of the reimplementation, it didn't provide an excuse for it.

Google has a strong tendency to have multiple parallel offerings in a field for a while before consolidating them (and, also, a history of botching the consolidation.)

My impression from second and third hand sources was still that YT Music implementation and brand was after GPM was asked to "code freeze" and the team directed to other projects (including some to YTM). That the products stood side-by-side for so long is only further indictment on the rewrite-the-world approach that it took them so long to reach "feature parity" enough that they felt comfortable sunsetting GPM, well after the writing had been on the wall, the development ended, and the marketing decision to change brands had been handed down.

The multiple parallel offerings thing is of course its own problem that seems to often indicate communications issues up/down the decision chains, but specifically with reference to GPM/YTM I heard it was more a symptom of a rewrite than one of those communication breakdowns. Though again, that's only from impressions I got from scuttlebutt I heard second and third hand.

Lync itself was a rebranding of Office Communicator, by the way.

Yes, that factored in as another reason it was a good analogy.