As a guy who fights the cost/reliability battle for consumer goods for my day job, I feel like I should point out threads are more expensive than bores. Seems like some companies don't bother to gauge their bb30 bikes though, so the failure mode gets kicked down the road to the consumer. External threads that wreck a frame if they're messed up would be a warranty/manufacturing spend situation I'd be trying to get out of as a bike manufacturer for sure. Lots of money potentially for something awfully easy to screw up.