If you can use facebook, youtube or twitter to reach lots of people, how could any one of them be a monopoly on reach?
Even though they are competing for attention, they each use different mediums. As an analogy, it's like only having one radio station, one TV station, and one magazine. There needs to be dozens of each for there to be a true marketplace of ideas.
Because more people choose to eat McDonalds burgers than the local dive bar burgers, does this mean McDonalds has a monopoly on burgers?
My local dive bar can serve me burgers whether it has a customer base of 1.000 or 1.000.000. A social network, however, cannot function without hundreds of millions of users. Otherwise it's an anti-social network.
As a result I can post my video to DailyMotion instead of YouTube but how am I going to build a following without engaging with Facebook, Instagram, or Twitter?
These networks require mass user engagement to be effective which precludes a myriad of competition. I don't think breaking these companies up as Elizabeth Warren suggested is the correct solution because it fundamentally handicaps their ability to function. But I think there does need to be regulation around how they do business which sadly does not exist.
I think the point is yes there are alternatives however given the size/reach of FB, YT, and twitter even those alternatives really aren't competing with them. They own the market share for what do and even many of those alternatives (ie mastodon) post on twitter or FB news or service updates. I'd say the alternatives don't even make up 5% use over FB, YT, or twitter.
Is it a monopoly in the normal sense of the word probably not, but the issue remains that alternatives are niche and truly don't directly compete. I think though as things like people being banned, creators being demonetized or the numerous other things that have happened in the last year to show users of these platforms the problems; we might see these alternatives pick up ground as these people with followings and clout get kicked off or decide to find alternatives. They get too big for their own good and in the process they will end up fragmenting their communities causing some to take alternatives serious.
Can you define a market each of them has a monopoly over? There are many popular video apps and many popular social media apps. Exactly what does each of them have a monopoly on? A network effect is not a monopoly. Being the exclusive provider of convenience for some specific group of people is not a monopoly.
For example, in some religious town, it's possible that the only way to reach a certain group of people on a Sunday afternoon is to go to the church. This does not mean the church has a monopoly on reach. Likewise, it's possible that where you live, the only place you can get a meal at 2AM is Aunt Ann's Diner. This doesn't make them a monopoly. Nor is the only sushi restaurant in town a monopoly. We live in a world of differentiation - every service provider that has a reason to exist provides something that others don't. This doesn't make everyone a monopoly.
Also, on none of these platforms is it trivial to build a large audience. And it's certainly possible to build a large audience through other means. For any given platform to have a monopoly on reach, people must be spending so little time outside of this platform that it's impossible to reach them otherwise. That's not a world any of us lives in. Even Youtube accounts for a very small fraction of time spent on watching videos and Facebook and Twitter are two of a large number of popular social networks. Snapchat, WeChat, iMessage, Weibo, TikTok, QQ, VK, Reddit, LinkedIn and Line to name a few.