The algorithms used by social media reinforces a person's own biases. The more you search and watch things, the more similar stuff is fed to you. This includes political biass.
Thier actually designed to feed you things that will maximize your engagement time, and a lot of the time it isn't what you asked for. This has led many to fall through social media rabbit holes and lies outweigh the truth when profits, clicks, and maximizing user engagement time are the goals. Researchers have even documented clusters of topics and videos where on leads to another, even if you aren't looking for it (like how searching legit vaccine info, groups and videos get anti-vax crap fed into it).
One of my own personal anecdotes is with Spotify, where I am frequently recommended country even though I don't listen to it or like it. On Youtube, Godzilla amd classic music lead to a video about the "human body vs a nuclear bomb." I didn't watch it, but it's easy to see how this unrelated, not searched for and a great gateway into the fear and knee jerking videos that meet the goals of the algorithms and have stirred violence around the world.