Okay, here's my crack at it.
Why was anyone even looking at lock designs other than lockbacks?
1. Lockbacks can suffer white knuckle failure. When you squeeze a lockback hard, your palm can sometimes hit the unlock button and release the lock. This is highly dependent on the person -- I know some people who swear they only have problems with mid-locks, and others who only have problems with the classic Buck 110-style end locks. There are a number of things the maker can do to eliminate this, such as scooping out the unlock button (ala Boye) or just choosing where to put the release button carefully.
2. Lockbacks are not self-adjusting with wear. As a lockback is used and the locking tooth wears, the lockup first becomes wobbly, then becomes unsafe. Other locks, such as liner locks and BM's Axis lock, are self-adjusting. As the lock wears, it does not threaten the lockup integrity.
3. Lockbacks are a pain to close one-handed. It can be done by using your leg, but that isn't as convenient as the worry-bead type one-handed liner lock action.
Of course, lockbacks had some great strengths, too.
1. A lockback can be made very strong
2. A lockback is ambidextrous
3. The lockback's spring holds the blade closed, allowing for safer carry and the option of tip-up or tip-down clip placement.
4. A lockback can suffer from white-knuckle failures, but only rarely suffers from spine-pressure failures, and (as far as I can tell) never from torquing failures. Less failure modes than liner locks.
By contrast, the BM Axis lock appears to address the 3 lockback disadvantages I mentioned. It also addresses the 1st three advantages, and doesn't suffer from any of the failure modes (so far!!!! testing still ongoing) mentioned in the 4th advantage. However, we've been debating whether there's a failure mode unique to slide-operated locks (like the Axis or Rolling Lock), where the fingers accidently engage the slide and release the lock.
Joe