1. it makes changing a tire more complicated, and time is money, the longer it takes to change a blown tire the higher the penalties
2. when a semi tire goes, it goes hard, as GP noted with this arrangement the cowling will probably shatter, requiring a replacement (not just a replacement tire) and the pieces taking out other tire. If the cowling does not break, it will funnel bits of tire straight into the next tires, blowing all of them.