He will now pay e.g. $1000. Tillable will offer $1100 upfront to the land owner and then "offer" it to the farmer for the low price of $1200. Since he can't just farm on some piece of land 500 miles away, he can either pay the new price, or stop farming.
Tillable offers no significant service here. It's not that there's a lot of land sitting idle because farmers and land owners have no way to come in contact, they are not solving a problem, they are just injecting themselves to extract rent with VC money.