I agree with the sentiment, but don't appreciate the way you put it (lacks nuance). I think it is obvious that developing custom design systems can sometimes give companies a competitive advantage, hence there might be a non-zero value here. Heavily depends on the product and the target audience.

In any case, the market has your answers. So many people are doing their own design systems. Can all this effort be caused by merely arrogance? There ought to be something else reinforcing this behavior.