I've been riding the same external BB since 2015. The only people I've ever heard of replacing their external BBs are hardcore mountain bikers or people with ex

I've been riding the same external BB since 2015. The only people I've ever heard of replacing their external BBs are hardcore mountain bikers or people with exotic weird BBs. It's nothing special, just a run of the mill Shimano BB-52. While the bearings are a bit more exposed, they're significantly larger which means they can be sealed better. In practice they are pretty well protected fully sealed bearings. There's not really that much of a reason they'd have to be less protected than internal bearings.