It's a cheaper version of a cable package that can be used by up to five google accounts that might not share the same physical household. EG a subscription with multiple premium channels and a good range of channels available in two households could easily be $400-$500 not including internet. YoutubeTV for a similar range of content would be ~$100.

The purpose of youtube for most consumers is to consume video content. Much of the professionally produced video content is TV shows and movies which obviously remains popular. This includes by reference content originating from a range of platforms HBO/Showtime/Starz/Paramount/AMC and so forth

EG you select HBO and Showtime as part of your package and can view the same content as is on MAX or showtime in the singular unified youtubeTV interface. Kind of a mixture of TIVO and netflix with a better interface.