Because the other apps offer something that tinder does not. For instance, Tinder has developed a rep for having a hookup reputation. This will make some girls hesitate to have it on their phone, but they might not feel about another app like say hinge. But, the biggest factor is the quality of matches a person gets. Tinder has rapidly moving into a "pay to play" territory, which translates into a person who is not willing to spend money getting less or lower quality matches. In my opinion, that is a bad business model. Think about if Youtube started charging you for every video you watched. You'd probably find a different company for video streaming. Tinder isn't on that level yet, but they have taken a few steps in that direction