Almost a decade of inexplicably stupid product decisions later, they've squandered their hugely valuable lead (and then some). I can't imagine why anyone would go out of their way to use any Google product whose usefulness is at all dependent on network effects (I've completely ignored the launch of Allo and Duo and, years after everyone else, have pretty much moved to FB Messenger as my primary messaging app). This is a pretty chronic Google problem that I noticed both from the inside and outside: their engineering and design talent are incredible, but the people responsible for the product and marketing side are evidently really, really bad at what they do.
This is part of why products like GMail or Google Search do so well, and products like G+ so poorly: you could be the only person in the world using GMail and it would be just as useful (and well-designed), while the quality of products like G+ depend less on their quality _per se_ and more on network effects, which Google's product/marketing is clearly too incompetent to do well.