This is a new restructuring from 2015 IIRC. It was Google inc that went public, and originally all the projects (including self driving car) were under google.

Alphabet was created later, together with splitting Wayne and a few others.

I don’t remember all the different triggers, and each triggers a different reporting requirement - more than 500 shareholders, more than $X billion paid to suppliers, stuff like that. Google, and later Facebook met all of them.