Comment by sokoloff

I may be able to do all the labor myself, but need investors because I can’t afford the capital.

I may be able to do all the labor myself, but want to ensure continuity beyond my ability or interest to do the labor myself. (Sometimes this is by my wish; sometimes by the wish of consumers of my service.)

I may be able to do all the labor myself, but not want to expose my entire net worth to the financial obligations of the company.

There are plenty of cases where a single person company makes good sense.