Apple Watch 1.0 may or may not be a flop. We don't know what sales are, nor do we know what expectations were. But ever-increasing retail presence among existing Apple partners is not evidence of failure.
If the ever-increasing retail presence was more like Apple Watches in bargain bins at the corner drug store, then I'd be inclined to agree with your theory. But that's not what we are seeing. All of these places so far (Target, Best Buy, B&H) also sell iPods, iPhones, and iPads, and some sell Macs too. They didn't used to sell these things, so when iPhone, iPad, Macs, etc. increased their retail presence at these stores, did you think those were doomed too?
In particular, Best Buy did a trial run in a limited number of stores to see how it would go. Months later, the trial ended and they decided to put Apple Watches in all BB locations. This doesn't make any sense if the Apple Watch was a failure. BB would be using up valuable retail space in all their stores for something that didn't sell during the trial?
Granted, it's possible. In a desperate move, Apple could be giving a sweetheart deal on wholesale pricing to the retailers such that the retailers would be making a huge profit on the watches even with low sales volume. But we don't have any evidence of that.
Anyway, my point is that retail expansion alone is not proof of failure. Wildly successful products also have ever increasing retail presence.