There are two things going on here. The first and simpler question is what is a valuable software product? For products where the user expects to pay nothing,

There are two things going on here. The first and simpler question is what is a valuable software product? For products where the user expects to pay nothing, like almost all social media, the answer is: the product with the most user-hours. Therefore products that attract many user-hours attract much investment. There isn't some kind of insidious conspiracy to push specific types of products: investors don't care, they care about how many minutes of ads they can push down the pipe (legally). The second question is: (again for products where the user expects to pay nothing) what products attract the most user-hours? It seems folks dance around and rarely confront what I consider to be the main explanation here and where the primary cause is: humans choose and prefer to consume and interact with content that induces in them a set of emotions. They generally choose to experience stuff that gets them upset, looks cute, inspires longing, makes them feel lonely, etc. If one categorizes the things that the consumer chooses as "problematic," where is the problem? The problem as stated is the consumer. One can't engineer a way out of that: folks have tried to provide alternative options and these mostly fail to attract heaps of users. To put this in the language of TFA: the addiction isn't engineered into the consumer. The addiction was there from the beginning: a million products were tried out, products evolved to better align with preferences, and now the products are "addictive."