Why do people say games are free on gamepass if gamepass is 17 bucks a month?

Yes, unlike an à la cart restaurant where each item that you purchased is tracked and billed separately then totaled up at the end. At a buffet, once you pay the $20 entry fee you can take as many food items as you want and there won't be an individual surcharge meaning that the individual items don't cost anything - which people often colloquially referred to as being free.