Why should I trust some arbitrary third-party OAuth provider? Why? Either I don't need this single point of failure and create an account on each and every ser

Why should I trust some arbitrary third-party OAuth provider? Why? Either I don't need this single point of failure and create an account on each and every service independently. Each and every service then stands for its own. If someone is able to infiltrate a service, it is impossible to infiltrate my whole personalty. That is different with a single third-party OAuth provide. First it needs a lot of trust, especially in terms of (cyber) security. Second: Kus why?