How? Well according to what I've read on the Internet the answer lay in a lack of focus. That is, the dev lead(s) seemed to keep adding in new features and then abandoning them before they were bug-free. Instead of focusing on getting the new features fit and polished and responsive to what their customers were telling them they just kept throwing more unfinished features into the product/service and then moving on to add in yet more unfinished features. The issue we've highlighted here in this discussion thread is just one of many examples.
Meanwhile I've moved on to using a combination of DigiCal, Aquamail and Google Keep for my portable office solutions. Let this be a lesson to software developers everywhere: Customers hate few things more than being forced to put up with something they don't need, don't want and can't get rid of. The classic example of this is the infamous Clippy "feature" that Microsoft bungled. Google takes the cake though; the fiasco that Google+ turned into was arrogance of monumental proportions. Their misguided insistence that every Google user of every Google product must have Google+ integration whether the user wanted it or not with no opt-out was just infuriating. You know Google+ integration is unpopular when a song with a refrain that starts "F@ck You Google+" goes viral (it currently has 3.6 million views). Note to Evernote developers: DO NOT try to emulate what Google did with Google+. It's a cautionary tale, not an instruction manual.
There's nothing like pissing off your user base to make them start looking for a replacement.