Because OKCupid overwhelms you with worthless information. It provides you with all sorts of stats that don't matter: favorite movie (re: movies I think will attract the person I want), favorite music (re: what bands might impress the person i want?), ridiculous quizzes (not that different from fashion magazine quizzes). Presented with this deluge of useless data on your partner, you can then filter on these worthless parameters (because why not? you're getting a ton of messages anyways, might as well filter on something). Anyways, after you've successfully gotten the number down to something reasonable you proceed to... make your decision based almost entirely on a picture.

The actual important thing to realize about Tinder is that it maximizes the only metric that matters: face to face contact. Everyone on there is on the same page: lets get together and in 30 minutes we'll have a WAY better idea of whether we vibe than reading a glorified resume online and going back and forth trying to by witty (often to then find out we have no chemistry in person!). Ironically enough Tinder actually uses technology to rehumanize the dating experience: its always been about going out and meeting people, Tinder is a simple extension of that, OKCupid tried to replace it with a "compatibility score".