That’s because your eyes do deceive lol. It’s to stop the drum itself from warping and the tension rods from bending. It also makes tuning the drum easier. The whole reason it’s done, is because top bass is usually cranked to a very high note.
Totally reasonable question, no need to apologize! We do it by cutting out the hoop portion of old heads, putting it on top of the new head, and then putting the rim over both. The idea is to give more room for crank each lug since with further out to start. We started doing it last year and felt like it worked really well.
