Failing to properly close a quick release is certainly foreseeable. It is not an uncommon thing to happen.
In the event that happens, the "lawyer lips" provide some protection against the failure mode of the axle falling out of the dropout.
But having a quick release that opens so far creates a different failure mode, of the lever getting trapped in the disc, and there is no mechanism to protect against that.....
.
Spotting this possibility in hindsight is easy. Anticipating the combination of circumstances that would lead to it is much harder. Part of the issue is that there are too many cooks in the kitchen, and it's possible that the engineer who worked on the initial design, and tests was wojing with other skewers and didn't see an issue. Later someone making or spec'ing skewers wasn't thinking disc, and wasn't worried about lever throw, since skewers are supposed to be closed.
Then somewhere along the line, someone at Trek opts to change hub or QR skewer vendors, and this happens.
This kind of thing happens all the time, in all industries, and isn't the result of a single act of stupidity or carelessness, but is the result of a chain or combination of circumstances, which would only matter in combination.
As I said earlier, I have no love of Trek, but I have no problem understanding how stuff like this happens, and find it much more forgivable than mounting disc calipers behind the fork, which has been SOP (with little protest) for decades.