There's a massively skewed ratio of men to women on these sites, probably around 10:1 men to women. As a result, women get spammed with no-content or offensive messages, driving many away. Those who do stay have to spend significant effort sifting through messages to find good ones, and inevitably a lot of good messages from decent men get lost in the deluge. Most dating sites are just glorified personal ads, no innovation at all. OKCupid is an exception with its quizzes and match percentages, but the percentages are inaccurate and OKC is filled with people who are just there for the quizzes.