A battery that eventually fails. Plugs that eventually break. All technology has a built in shelf life, whether wired or wireless.
And yes, these don't sound quite as good as my £120 B&O headphones, but there really isn't much in it. In fact the only real difference is a slight hiss in between tracks. I like the sound of them, they are enjoyable to listen to and the convenience is well worth it.
And they are a quarter of the price.
ETA: I would happily put them up against any £30 wired headphones. I would say they would easily beat them, two people who have tried them against airpods have preferred them, the price was a consideration in that TBF but the sound is much better than you would expect.