"it makes no sense" literally every social media site in existence has the block feature, and the reason is to help people prevent harassment. Elon is like a fucking toddler, it's obvious he just wants to get rid of blocking because he's pissy about being blocked by other people.
Actual answer: back in the day the sealant that farmers coated barns with often had iron oxide in it because it helps prevent rot and mold, and the iron oxide would turn the sealant mixture red. Now people just do it because it's a tradition.