Jorads are a fashion choice. Stop buying Nike and get some engineered shoes from New balance. The yellowing is one of two things. The material used is not UV stable, the more it is exposed to the sun the yellower and hazier it will get. Secondly there may be nicotine in the air, staining it. The unlikely the base material has acid and now enough time has passed for it to be a problem. Similar to regular paper, it turns yellow in 10 or more years too.
Putting the shoe in a oxygen free and UV free environment should stop this from progressing.

Sea glow should reverse the yellowing