This is Vic Gundotra's legacy and perhaps the first major strategic decision Larry Page made in the post-Eric Schmidt era and it was the design and launch of Google+ and (IMHO) it marked a turning point in the company's culture. Internal resistance to aspects of G+ was enormous. People outside the company get this idea that Google acts as some kind of singleminded (possibly nefarious) entity when "herding cats" is so…
Trying it at all after realizing it was not going to be complete. I think the unified account was an all-or-nothing strategy, and they met with early resistance from every dedicated user silo on all of their previously very separate products.
But instead of launching some big unified account thing to really force Google+, they did a kind of half-assed thing. Some accounts migrated and auto-signed up, there were some weird account-links, people had multiple accounts (youtube, gmail) etc etc. They backed out, pandered, etc. It was an absolute shit-show from the perspective of a power user.
If someone would have had the prescience to say "our products are too silod for a successful merger" at the onset, and then either spent 5 years slowly breaking down those silos FIRST, or just tearing the walls down AT ALL, it might have worked.