Hey look, a rock! I patent rocks so no one else can use them.
DNA is data. When the data has certain characteristics, it can be protected as intellectual property. Same for the data stream that makes a music recording or photograph, or a computer program.
Sure, if you rearrange it to produce something new and useful. But if it just sitting out there in the wild you can't claim it as your own. Some of those trying to patent DNA sequences are like my pet cat who picked up a bird that had knocked itself out on a window and carried it around like she was a mighty hunter.