It makes sense for Match Group to specialise their offerings based on the types of people they think might want to date - e.g. quick flings vs more serious relationships.

Okcupid used to be the only good option, but it got increasingly worse since match.com bought it. They recently did another overhaul and now it's so bad that it feels like they're deliberately trying to kill their userbase. Which might actually be true - it's probably better for match.com from a business perspective to kill off some of their less popular offerings and force the users to migrate to Tinder. The network effects and hence the potential monopoly are nothing to scoff at.