This isn't to say that external BBs don't or can't last, but my long term experience is that good quality classic cup/spindle BBs outlast their modern replacements by a large margin. It used to be rare to replace BBs or bearings due to wear, which has become a more common repair with the advent of new and improved BBs.
I suspect that the key difference is rigidity. Bearings are very sensitive to misalignment, and flex in many of the current BBs may be costing bearing life.
OTOH - modern BB systems are much lighter, and that , even at the cost of shorter life may be worth it as a trade off.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.