Its called field tile. And there has to be a place downhill to let it run.
Very expensive to put in.
Most of the hills/hilly grounds are planted. Its the lowlands and level grounds that arent.
Given that 1 inch of rain over a square mile is approximately 17.4 million gallons of water, finding a place for it all to go is challenging.
$2.00 a foot to tile out drainage. My Dad has 500 acres in Minnesota. All been tiled out for decades.