I saw something the other day that is unfortunately rare these days, a company HAPPY with IBM/Lotus Notes..
It turned out to not be what they had but what they DID NOT have, they had no limitations on who could create databases on the servers* also they all had the full Notes client with the designer, so departments created apps just like they did in the old days, they took the standard templates and altered them to fit their needs just like the do with Excel spread sheets, MS Access databases and indeed to some extend Sharepoint,
Notes had not become controlled by the management and techno elite, it was used by everybody, there was no fighting for “engagement” as is the case for modern social platforms, it was achieved organically without the need for HR and marketing to stick their hoof in.
So if you want my opinion about the real reason that notes is not as popular as it used to be, blame IT and management for wanting to control everything, for taking the users that want to be pioneers and making them drones.
*Though there were a few sane guidelines