Facebook Dating isn't a standalone product, so people are likely going remain on the app even after they get into a relationship. The service only exists to funnel young people into the Facebook ecosystem. The dynamic is very different from a regular dating app where once you get somewhat serious with someone even having the app still on your phone will be seen as a massive red flag.

And Facebook itself has been used as a dating/matchmaking service since well before Facebook Dating or Hinge/Bumble etc. were a thing.

It's basically the original purpose of Facebook (some might use the term "stalking" over "dating" however).