One of the big challenges is that Twitter is largely geared towards people looking to engage on topical issues in a public forum. If you're an expert in a particular area and consistently engage with other experts in a public forum where the occasional random user chimes in then Twitter has a value proposition for you. I mean it's right there in the platform... people "follow" you, they're not your "friend" or "linked" to you. You need to say something that people are interested in following.

The problem is that most Internet users don't fit into this bucket. They have things to discuss and share with a small group of family/friends but beyond that don't have much to say, to the broader world. These are the users that flock to Facebook, Snapchat, et al.

Until Twitter finds a way to engage the everyday average Internet user then they'll struggle to grow or create a meaningful value proposition (the $$$ is in advertising to the masses, not the engaged thought leaders).

The data on users indicates Twitter has likely peaked in terms of attracting these engaged users (data also indicates a lot of these "active accounts" are fake / bots / spam). Until that changes Twitter will be in trouble as it has no viable long term business model.