Yahoo and Bing are not significant Google competitors. They aren't even independent — Yahoo search is Bing.
As a social media user, you're not the customer, you're the product.
Take a look at all of the companies where a court determined that the company abused its monopoly power.
Every single one of them had "a myriad of other players" in the market.
So the existence of other players doesn't mean that Facebook doesn't have market power, it doesn't mean that FB isn't a monopoly, and it doesn't mean that FB can't abuse its market power.
Only a few hours ago, jwz (who blocks links from HN - fwiw, we are HN products) at https://www.dnalounge.com/backstage/log/2018/04/10.html wrote:
> Advertising anywhere that is not Facebook simply does not work. We keep trying and keep getting nowhere.
> We hear that from other promoters and venues, too: everyone says "Yeah we only advertise on Facebook. Nothing else does any good."
> I hate that this is the case. A lot.
This is the sort of comment you see if a company has market power, where switching to other players is not an option.
On one layer, they offer a social networking site to people, who become users. Then they take the information and sell it to advertisers to make money. Without the social networking site, Facebook wouldn't have its advertising business. There are more, I'm sure (governments are sometimes customers, for example).
There is only light competition for the advertising right now, but I'm going to guess we'll figure that stuff out as time goes on.
As far as the social networking itself, there are options, but none that can replace facebook's user functionality. There isn't anywhere robust enough to make change feasible. Instead, you can replace parts of facebook with other things and get partial functionality Your mother probably won't download a weird app just to talk to you instead of using messenger, for example, and your sister probably won't send you the pictures of the kids as often.
Google on the ads front.
Telegram and Apple (iMessage) on the IM front. (Not sure this one really counts, though. Is IM a "front"?)
The answers you gave for MS / Google would have gotten the same kind of interruption from the senator.
Microsoft's competitors are Apple on the hardware and software front, Google on the search engine front, Atlassian on productivity tools front, GitHub on the repository/code storage front, AWS on the cloud storage front, etc. I assume Microsoft's core solutions are their OS, their productivity tools and cloud.
Google's competitors are Yahoo, Bing and Duckduckgo on the search front. Garmin, TomTom and others on the map front, etc. And perhaps everyone on the email front. Here I assume Google's core tools are search, email, and maps.
Facebook's competitors are... Instag- oh right. Uh, Snapchat, I guess?