Why, for instance, should I pay as much for a season of X-Files reruns as for the production of an entirely new series of Stranger Things? Why would I pay as much for episodes of The Sopranos, that I have already seen, and have on DVD, instead of another new series of Lillyhammer? I wouldn't, and neither would Netflix. The original content is a reminder to the owners of distribution rights that Netflix is the one who owns the ball, and they're the ones that will be taking it with them if they decide to go home and play alone.
And Netflix originals are getting nominated for Emmy Awards, in competition with AMC and HBO shows. Producing exclusive original content was absolutely the correct play for Netflix at the time they decided to do it, and remains so for the present.
I've been looking into film and TV production for years as an outsider and come across several mentions that Netflix pays extremely well and is incredibly picky about their productions. So they're in the game to play for keeps it seems. "Come for the Netflix originals, but stay for some binge TV or the occasional random flick like a big on-demand shifting library!" as a tag-line sort of works.