I didn't intend a comparison between Gmail and Hangouts, just to say a whole lot of people already had the required account.

You definitely had a rougher experience with it than I did, but my main point is Google launched it, didn't seriously iterate on it, and gave up its strongest distribution channel at the first sign of pressure from carriers. Since they keep launching messaging products, I must conclude they want to be in that space and it was foolish of them to squander their best opportunity.