You may not recall but the TV manufacturers used several big sports venues over 10 years to showcase HDTV.
I recall the Barcelona Olympics featured, years before sets were on the market.
They sponsored every major soccer event -- World Cups, Uefa Euros. In the US, it wasn't just Super Bowls but when they first started broadcasting weekly games in HD. To this day, Sunday and Monday night NFL games are the most highly rated TV broadcasts.
Sports not only paid for all the sets to be upgraded in homes from analog sets, they paid for a lot of the production equipment. HD movies were probably a distant second or third.
So if they want to sell a lot of 4k sets, they have to demo sports in the best light, even if it's up scaled.