There's 3 glaring problems here.

1. There's a steady stream of unmarried individuals so as you match people up there's more people (either just from growing older or divorce) that can use the app.

2. If you don't already own a dating app, then even if you cannibalize the market you can still make a large sum of money. Akin to mining all the gold in a plot of land; sure your company needs to close once its gone but you made money in the interium.

2.5. If you do already own a dating app, if you're known for not working then people will stop using the app and go to a competitor (assuming you didn't buy them all ...)