Call it the value of experience, and lacking that, 3GB is a great choice for a midrange GPU. Then you use one, you learn its not all that rosy as the reviews and benches told you, and you make the better choice next time. Or you're thát casual in gaming that you never touch a game that hits a limit or accidentally never use settings that hit a limit. In those edges cases, yes, 3GB is fine.
Its not like there aren't any alternatives at the same price point. Back when the 780(ti) and 7970 were hot, that was different. Today, its silly to pick one. Its simply not the preferable choice especially given the often tiny price gap for something better.