Completely speculating, but when an App Store review process can drive business decisions (we have to push the launch of X back because we're having trouble lobbying Apple to approve our changes), it's reasonable to see a second app as doubling the likelihood that you end up in that situation. And even if it weren't for the review processes, would every launch be at the mercy of reporters saying "this isn't supported on my watch, so..."?
It's also possible that each company simply lost all the people who knew the watchOS APIs, and the incremental revenue generated wasn't worth hiring for that role again, or trying to convince someone else at the company to add it to their scope.
Perhaps, as well, there was an expectation that Apple would be the one encouraging Uber to maintain and build the app, and give them favorable treatment on the App Store review processes as a way to sweeten that deal... and then when the larger relationships started to become more acrimonious, any ideas here fell by the wayside.
It's also possible that each company simply lost all the people who knew the watchOS APIs, and the incremental revenue generated wasn't worth hiring for that role again, or trying to convince someone else at the company to add it to their scope.
Perhaps, as well, there was an expectation that Apple would be the one encouraging Uber to maintain and build the app, and give them favorable treatment on the App Store review processes as a way to sweeten that deal... and then when the larger relationships started to become more acrimonious, any ideas here fell by the wayside.