That's a business decision. They made a decision to go for quantity over quality, and that's fine for the short-term.
I think Netflix simply didn't find the right balance. It's okay to have cheap shows to fill in the blanks, I mean, I enjoy some of them. But the biggest problem is that they give up on pretty much every other more "artistic" work too easily; even when these can only become popular years later.
Also you can buy the rights to old good stuff. Might not make good business sense (some (weird! senseless!) people will only watch new stuff) but it'd please me. My favourite stuff's all older than I am (i.e. I don't think you can claim it's just fond childhood memory or whatever) and there's plenty of greats I've yet to see, why restrict myself to this year's crap (and perhaps hit or two).
The entire structure and model of the business leads to produce exactly what Netflix makes. Season after season of mediocre TV that keeps people subscribing, using the same formulas over and over for more growth. Just like traditional TV at this point.
Occasionally they'll get a good indie hit but that's about it. It's telling that much of the best content, like Dark or some of the South Korean shows is not coming out of the typical studios.