That's normal wear and tear for over-ear headphones. You should expect for these ear cushions to eventually wear out. They are constantly rubbing against your glasses, earrings, headband, etc. as well as just your ears/head. Unfortunately, they should be considered consumables. Fortunately, as others mention here, there are multiple first-party and third-party replacement pads on the market, so you can replace just the pads as they wear out.