Also, Steam is a middleman that developers other than Valve have to pay
developers make 30% profit on retail sales, they make 70% on steam sales
it's convenient having a game system where you don't have to worry about requirements
it costs less to have a good PC than to have a normal PC(everyone does anyway) and a game console
plus chillin' on the couch it's good times.
you can connect a computer to a TV and chill on the couch with a controller too...