SSO concentrates convenience and consequence

Single sign-on means one login opens everything, which is both the benefit and the risk.

It genuinely improves security in most organisations: one account to protect properly, one place to enforce MFA, one place to switch off when somebody leaves. It also means compromising that one account compromises everything at once, and that an outage there stops all work rather than some. Concentrating is usually the right trade. It is still a trade.