There's no catch. For a 12-month 14TH contract you'll be getting around $30/day worth of bitcoin. And miners do this because they get paid upfront. I.e. they can buy a mining rig with the money you pay them for a one-year contract. That lets them get into mining business with practically zero investment. They just have to uphold that contract for one year and then they own the mining rig.

Why wouldn't they let you buy them a mining rig? All they have to do is to run it for you for one year. So it's a WIN-WIN; you profit from mining without all the hassle with having an actual mining rig, and they get a mining rig for running it for you for one year.