Why hasn’t my second stimulus check arrived?

You can count on the fact that it is delayed in the mail. The postal system is still recovering from 'ship-ageddon' and it will eventually arrive. There is no delay in processing them on the government's end. Some people actually got them earlier than announced and others are still waiting and probably will continue to wait. It depends on the logistics of reaching your location, weather and traffic events in your region and overall volume.