Not because you're wrong, but because any competition that comes up in Europe gets bought by the giants to the west, usually before they're globally known though sometimes not; I'm sure it's not entirely unknown that Skype was purchased by Microsoft at least, that was a pretty big player at the time.
In terms of general tech companies there's loads, including Shazam, iZettle, Momondo, Gamesparks, spider.io, Mojang, Apiary, Sparrow etc;etc; 52 by Apple/MS/Google in the years 2011-2016.
I'm honestly surprised Spotify remains.
A European social network has a really high barrier to entry compared to the US ones, sure, but all that meets them if they're successful is an acquisition- or at least that does seem to be the case with most European tech startups.
To your first point: I think the closeness with the CCP and closedness of the country would be fine points, my general feeling is that the US is a lot more clandestine with their methods (Snowden wiretapping of google revelations notwithstanding: most orders in the US come with stipulations that you're not allowed to speak of them).
Regarding the "openness", I feel like the US is battling it with Sinophobia, I mean, based on the former Presidents words at least; rather than an outright ban as the Chinese are doing.
What do you think?
What's more, Europeans are free to develop their own social media platforms, and in fact I wonder why they haven't been more successful to date; there's plenty of software talent and cultural depth in Europe. It would be great to see more competition.