It started with ArcGIS Pro, and has recently exploded with almost all web based products.
For a long time users had asked for a 64 bit version av ArcGIS för Desktop, the answer finaly became ArcGIS Pro, a new 64-bit application. Pro was not to replace ArcMap, but ArcMap was never going to become a 64-bit application. So yes, Pro IS the replacement of ArcGIS for desktop in the long term. But ESRI couldn't say that because it lacked so much functionalty that ArcGIS for desktop had.
I actually don't know if Pro is a fully replacement for ArcGIS Desktop now five years after it was released. My feeling is that ESRI put's more effort to develop new fancy features for Pro than adding the missing ones from ArcGIS for Desktop which could explain the long time it takes until most users can actually migrate to Pro.
Maybe there was a dead end for ArcGIS for Desktop, a totally new product was necessary to keep it up to date, but I would prefer a more finished product before relaease.
Now when I really have to let go of my FlexViewer, the new Experience Builder is released. So I thought maybe I should go straight to that, but not very suprisingly it lacks so many widgets that it's not an option. Therefor I have to go for WAB wich is officially not supposed to be replaced by EB, but we all know it is in the long term. And ESRIs development will be focused on new functions i EB and not WAB.
Let's take one last example, "grouping layers in a web map", tons of users have been asking for this since AGOL was released many years ago. It seems like a pretty basic functionality, but probable the web maps in AGOL was written in a way that made it really hard to accomplish this (otherwise it'a a disaster it hasn't been implemented). Now finally it seems like it will come as a feature in the new Map Viewer. And I guess many users will shout out "at last we can group layers!" But then (if I've got it right) be very disappointed when they realise that if they want to use this basic functionalty, they have to use the new map viewer och consume the map in one of the new apps based on API 4.x that still lacks a lot of other basic functionality. And probably will do for a couple of years while ESRI adds new fancy features to the new products that many of us can't use due to the lack of functionality, forcing us to stick to the old apps.