1. The US economic regulation regime allows one or a few companies to hold an amount/quality of power, beyond which the FTC is supposed to get involved and break up the companies so that power isn't concentrated. This exists because pure capitalism quickly results in one winner, which makes for zero incentive for it to compete/improve/lower prices/increase quality. The fear of anti-monopolistic action by the FTC is low enough and actual action is rare enough that lots of power is unchecked.
2. Humans like bright lights/shiny objects (gambling), feeling tribal/us-vs-them (rage bait wins, negativity drives engagement), are easily exhausted by or ignore options (overwhelming acceptance of defaults), etc.
The above, either in combination or separately, combine to drive low quality computer experiences. Marketing/advertising alone drives an incredible multiple profit compared to actual quality of product/service.