why do people assume ocd is just being a perfectionist?

Oooh I like this question! My answer has a few parts: 1) Media representations of OCD are largely limited to contamination and perfectionism symptom clusters. You see a lot of stuff about people with OCD straightening things to perfect 90 degree angles, living in extremely tidy spaces, and spending excessive amounts of time doing and redoing basic tasks to do it “right.” On the other hand, you see little to no representation of intrusive harm or sexual thoughts, scrupulosity, social obsessions & compulsions, existential OCD...the list goes on. Hence, most people who don’t have any experience with it or relationship to someone with it only really are exposed to the representations of OCD as germaphobia and perfectionism. 2) Most people do not understand the extreme, life-interfering level of perfectionism that warrants an OCD diagnosis. It’s one thing to LIKE/PREFER your picture frames leveled and even, but it’s a whole other ballpark to NEED literally everything else in your life to be leveled and even too, and yet another thing to spend so much time straightening things in your living space that you cannot leave the house. The average person does such things because they just like them that way; a person with OCD does such things to the extreme because if they don’t do them, their anxiety becomes insurmountable and unmanageable. 3) A primary characteristic of OCD is highly rigid thinking patterns. This cognitive rigidity is reflected in the need for things to be “just right” and done in a very specific way. The OCD brain has difficulty being flexible. In this way, all OCD does somehow reflect a sort of perfectionism, although in very diverse ways in relation to a wide variety of obsession themes.