Guinness does come in cans, and there are a few other better-quality beers. It's not all Miller and Coors.
(Of course, the very best still comes in bottles only. But there's some very drinkable stuff that does in cans.)
Last time I got a Guiness it came in a can (they didn't have anything better). And they served it by upending the can in a glass and leaving the can in there while the glass filled. I told the server to never give it to me that way again unless she KNEW that can had been cleaned before hand. I KNOW where my bottles of beer have been, but where has that can been stored and what (rodent or insect or dust) has gotten on it?

? Total gross out for me. But I have way too much imagination for my own good.