Lotus Notes was too big, too self-contained, and too weird to be "Something bigger than a weird email client." One facet of being too self-contained was that it had its own user interface paradigm, which was different from the operating systems it ran on. In other words the product decisions that would've made sense in an IDE or maybe a CAD system were bad product management decisions for a groupware product. Notes also had its own self-contained application development language and runtime. That is reminiscent of 4GLs. Remember 4GLs?
Maybe there is a parallel reality where groupware is as important as web browsers, but not in this universe.