It's the networks cameras, and they're locked into massive investments in older broadcast technology. 4k cinema cameras that have a million times better image quality are a fraction of the price of the old dinosaur tv cameras.
The shots they cut away to on the field that look cool as hell are often freelancers with a $2,000 camera and it looks a million times better than the $500,000 camera shooting the sideline...
But yeah, they need to get with the times.