Why is there a sheet of paper in packages of minced meat?
The paper isn't for you. It's for the robots.
Packaged ground meat like that is ground, portioned, and packaged automatically. The blocks of ground meat are formed by extruding them into an endless strip which is chopped into blocks and moved around on conveyor belts. To prevent the meat from adhering to the belts or falling between them, the strip is formed on a roll of waxed paper, which is sliced with the rest of the meat and remains on the bottom of the blocks through the remainder of the processing. It's not important to remove the paper, so they don't bother.
You can see an example of the technique at https://www.youtube.com/watch?v=wPRea1f8sg4 .