Much will be made of Twitter's inability to monetize its traffic. To be fair, one might add all the other interesting firms, lead by apparently capable leaders, who likewise have failed to create robust ad-supported business models over the last decade or two.
Perhaps it is worth keeping in mind other markets where market share is a duopoly. Between them, Google and Facebook earn about 52 percent of all mobile advertising revenue, each having an order of magnitude more net mobile ad revenue than the closest other provider.
Facebook and Google also are getting 76 percent of all the net new advertising growth, according to KCPB.
In that sense, the mobile ad market is nearly as concentrated than the telecom market. Looking at internet access subscribers, for example, two firms--both cable companies--control 60 percent of U.S. internet access accounts.
Subscribers at End of 3Q 2016
Net Adds in 3Q 2016
Other Major Private Company**
Total Top Cable
Total Top Phone Companies
The point is that Twitter is something like an overbuilder (third provider in a market dominated by a cable company and a telco), where getting as much as 20 percent market share normally is a major achievement.
The “reason” Twitter has so much trouble monetizing its business could well be for the same reasons that smaller providers (and even some big companies) find it so hard to gain scale in the telecom business.
Where durable duopolies exist (for internet advertising, mobile advertising or telecom services), it is hard for provider number-three to get a foothold, much less challenge the market leaders.