They don't directly tickle the reward center of the brain like social media does, cf. e.g. "Brain anatomy alterations associated with Social Networking Site (SNS) addiction" [0].
This is by design, btw, cf. e.g. "Digital Madness: How Social Media Is Driving Our Mental Health Crisis--and How to Restore Our Sanity " [1]; not itself a primary source but it seems to be well received.
My point being, it's like cigarettes with a message. The message being divisive in all likelihood, in order to override rationality with emotion and increase engagement. [2]