Washing was a gross cultural achievement of man on the way to what we call "civilization" today. Like so many achievements, it has to put up with doubts from people who look back in confidence and think how much better everything used to look in the rear-view mirror. In the stone age, for example: so much fresh air! And then the food! All organic! In reality, a stone age man was so burdened by diseases and parasites and stress and the extremely harmful environmental influence of "bad weather" that he was happy when he lived to be well over 20 years old.
Earlier everything was dirtier
Currently, the pink back-glasses turn to denim jeans. What a great material! In the past, a handful of people used it to build up the whole of america, which had been conquered by these savages! That was only possible in jeans. Who had none, fell from the skyscrapers, which had to be built. The jeans were therefore or on top of it in the USA always probably the most worn motorcycle trousers. In the more thoughtful germany, in younger times, the aramid-strengthened jeans with protector pockets slowly managed to become the accepted motorcycle summer pants.
The back view glasses are looking at how people used to wash their jeans. Probably rarely, and if, then only in dirty places, because at that time not yet everyone had a washing machine. But it was certainly not because of the washing machine! No, the old sages simply knew that it is best never to wash a pair of jeans, and this must be immediately proclaimed as truth in forums. In these forums are then tips in it like put in the freezer to kill the worst odor. Above all, there are songs of praise about how good it is for the fabric. Since good motorcycle jeans carry crisp price tags (the reference rokker costs 350 euros), I understand every motorcyclist who is interested in this discussion.
Short and direct: keep a pair of jeans longer if I don’t wash them? Yes. They also last longer if you do not wear them. Mechanical stress from washing or wearing puts a strain on the fabric, which will eventually need to be replaced. That is just a stupid argument. Brake pads also last much longer if I never brake. The question is rather, whether washing brings a significant advantage, which outweighs "everybody hates me because I stink". In my experience: no.