Platforms need your attention because they want you to create more connections to manage.
An established strategy in this industry consists in (1) attract people by promoting the advantages and the benefits of the service (2) transform people into users by convincing them to allow the platform to manage their connections (3) seduce users to create as much connections inside the platform as possible until the point that the mere idea of changing to another platform is inconceivable, because the work that implies exporting all the connections is overwhelming or simply because there is fear of losing them, what in summary, can be described in this one sentence: turn users into prisoners by kidnapping their connections.
What is happening is similar to the following situation, and is not exclusive to tech platforms.
Imagine. You are invited to join a community, they give you a place to stay and all the tools and resources you need to decorate and fill your new house so as to make yourself comfortable. They also throw parties and organize a wide variety of activities to create bonds within the community. But the moment you want to move to another community and you ask for the way out, the responses are evasive or the procedure is extremely inconvenient. Moving all the things you built here by yourself is exhausting, so it’s easier to stay or leave everything behind.
Independently of the particularities in the strategy used by each platform, what all of them need at the end in order to survive is that you use their service. If you don’t know them yet, they have to introduce themselves first. If you already have a relationship with them, they will encourage you to keep using them. In both cases, they need your attention to start the pertinent discourse.
This is why we can say we are living in an attention-based economy.