So at best, the developer is incentivized to have the user find someone to date in the short term and have the relationship fail in a manner that doesn't reflect poorly on the dating site. And it's not really feasible for the dating site distinguish between "will successfully date for a few months" and "will successfully date for a lifetime".
You could apply the same logic to any long term purchase. Dealerships only sell lemons because they want you to come back and buy more cars. Recruiters only match you with companies that you'll definitely want to leave because they want to match you again. Realtors only show you houses you'll hate because then you'll want to move again.