People hated it because Google for some reason decided to force it into YouTube by forcing you to link your YouTube account to your G+ account. Remember that stick figure tank guy that was plastered over every comment section?
I believe that’s mostly what killed Google Plus. People were introduced to it in the worst way possible, so nobody actually cared to try it out, even if it was technically a good product.
This was also introduced in the same moment as a bunch of real name initiatives from multiple companies. People were rejecting it based on what it demanded compared to what was offered. It also killed or force reworked other Google products that were working fine to end users (e.g. Google Talk).
In my eyes it was one of the key moments that put them on a downward trajectory in public opinion. So while it might have had the right features the rest of the deal sucked, and people were already tiring of social media overall.
I believe that’s mostly what killed Google Plus. People were introduced to it in the worst way possible, so nobody actually cared to try it out, even if it was technically a good product.