This article is a good read, but this following excerpt is an angle I would love to see a more expanded look into:

Indeed, the profit models of many online-dating sites are at cross-purposes with clients who are trying to develop long-term commitments. A permanently paired-off dater, after all, means a lost revenue stream. Explaining the mentality of a typical dating-site executive, Justin Parfitt, a dating entrepreneur based in San Francisco, puts the matter bluntly: “They’re thinking, Let’s keep this fucker coming back to the site as often as we can.” For instance, long after their accounts become inactive on Match.com and some other sites, lapsed users receive notifications informing them that wonderful people are browsing their profiles and are eager to chat. “Most of our users are return customers,” says Match.com’s Blatt.