Todo's appearances in the JJK manga are scattered. It depends on the specific storylines and conflicts. Sometimes he's in the foreground, and other times he makes cameos to add to the overall narrative.
A true simp story could be about a guy who always buys his crush expensive gifts without expecting anything in return. He just does it out of pure adoration.
It could be that their storylines and personalities offer an escape or a form of entertainment that resonates with you. Sometimes, we simp for them because they represent something we wish we had or could be.