It's a mix of bad writing ability, contrived arguments (coming up with weird hypotheticals or simulating what an opponent would say), cargo-culting rationalist thought leaders (Yarvin, Scott, Yudkowsky, gwern) and the concealing of unsavory ideas.

There's also a culture of not knowing when to stop posting and touch grass - when all your friends are way too online and probably also rationalists and much of your identity and status is tied to online posting, you invest a lot in cultivating that social identity and signaling to your community, even to a degree that would look unhealthy to normies.