I don't have the numbers on how many knives are locking versus non-locking, but that's really beside the point. Locks are not a fad, and I'm not sure why you keep asking that (since it's not a claim I ever made). The thing I am responding to was your comment that slipjoints are not popular, when by every metric, they are. Secondly, both Benchmade and Spyderco make nonlocking folders, which kind of reinforces my point that they're a popular style of knife. The Italians sure love them, with virtually every major Italian maker also making a huge number of them.
In any case, the reason why people like locks is because they give people who aren't really good with knives a false confidence that they can abuse the tool and be safe, because the knife won't unlock and injure them. Very few lock mechanisms on the market today can say they've had zero failures. Spyderco, Buck, Benchmade, Zero Tolerance, virtually every American brand has had people come in here claiming Company XYZ's knives suck because their examples failed. I hate to be the bearer of bad news, but that is statistically insignificant. The Adamas specifically, they've sold tens of thousands of them over the model's lifetime. If it's such a terrible design, why aren't we hearing about massive numbers of them failing? The Adamas specifically has held up to "hard use" by plenty of people who own them, myself included. So now what? Which anecdotal story is true? If the OP says "The Adamas sucks, I had two examples fail on me, and I know some guys who also had theirs fail", a logical person is going to start looking at (man, I dislike having to repeat myself) the common denominator. Plastic zip ties? I've cut plenty of those with mine. So have others here. So, does one guy's experience override all of the other owners of an Adamas who can attest to having used their knives hard without issue?
It boils down to this. The user. When some people hear/read "hard use", they think "That means I can abuse this knife and it'll take it!" "Hard use" to many of us here on this board still means "Using this tool as a knife", not a prybar, a screwdriver, a lever, or anything else. Remember, a folding knife is a handful of disparate pieces bolted together, with several possible points of failure. For those of us who have used the knives hard as knives, interesting then, that we haven't seen the issues OP has seen, no? "But, but, the OP cut some plastic straps!" And? It's entirely possible that they were shoving against the medium those straps were strapped against, and somehow actuated the lockbar forward on the backdraw, unlocking the knife. That would be 100% user error, and could have happened.