Capitalism is how all of our shit works, so it’s lacking in specificity but also a pretty accurate thing to say in many situations.

Why is social media shit? Well, “the platforms are incentivized to demonstrate growth in profit to their investors, so they optimize their system for maximal engagement and retention over time, transferring the same incentive to creators, so many creators who would have made better work before desperately churn out poorly made material about whatever is popular and other, more interesting content is ultimately less common on the platform, with the root cause being the constant need for a growth in surplus in all areas of social production” is a better answer, but “it’s capitalism” is still an alright start.

But this is true: the Tragedy of commons (AKA «keep profits, externalize costs») is a common thing in unregulated capitalism. Regulated capitalism tries to solve it with rules, lot of rules. Socialism tries to solve it with bureaucracy, lot of bureaucracy. Communism (no profits) and monarchy (monarch eats the costs) are somewhat immune to this problem.