Originally Posted by cuda2k
Bigger axels, bigger bearings = siffer, longer life. Keeping the bearings on the inside meant smaller bearings for larger axels which greatly reduced their life. Bigger bearings required thinner axels (think older square taper) which flexed more. It was a trade off situation that external bearings solved to a large degree, or at the very least elevated the baseline for the trade off.
Or you could just increase the size of the BB shell ala Canondale. But then you've got the non standard problem.