Why don't cast members just... not get married?

I would love to understand the contractual obligations of this show more. I find the pressure to commit to marriage after six weeks to be so strange when there doesn't seem to be anything barring them from continuing to date without getting married just yet.

To me, that would be the win-win — get to the finish line, commit to one another, and just date like normal people. But why do several of them actually get married? Is there a monetary incentive to marry at that moment? Is that the only way you keep the ring (which I imagine was gratis)? Why would you rush a wedding (that likely isn't the wedding of your dreams) when you don't have to?