I don’t think anyone knows for sure, but my own guess is that the company has never (and that includes before the Samsung acquisition) been driven by an engineering perspective. It’s always been driven by a marketing perspective.
(That was obvious for years when the original founder, who was not an engineer, kept telling the story of what use case had prompted him to begin the whole SmartThings journey, and to this day that particular use case still is not solved by the SmartThings platform. Because it had to do with problems occurring when the power went out at a vacant vacation home and all SmartThings notifications still run through regular Internet rather than a cellular connection, so no power means no remote notification.)
The end result is a system which looks great in a scripted demo. And that’s still true.
But it is rare for edge cases to be documented or even tested. The kind of things that engineers find fascinating just aren’t a part of the development culture. 
That doesn’t mean it’s a bad system. All home automation systems have pluses and minuses, and some of the pluses for SmartThings are really cool. Including a very nice app and a willingness to be open to all kinds of third-party devices.
But it does mean that it can lag behind its competitors in both engineering quality and generational features, particularly the features that don’t show up on a 20 foot display behind a keynote speaker.
And at the time of this writing, that’s even more true for Z wave.