That mechanism also exists, notably in Vista and 7 there were a number of older applications where Windows would display a warning prior to running it that the

That mechanism also exists, notably in Vista and 7 there were a number of older applications where Windows would display a warning prior to running it that the application has known incompatibilities and may not run correctly. However, a user who just upgraded Windows and half their programs stop working will simply not upgrade. In many cases such dodgy applications are also never fixed because the vendor doesn't exist anymore, doesn't care, or the flaw is in some library they use and they don't really want to invest that much time to change it. Besides, detecting such behaviour is pretty much the same as fixing it with a compat shim, since you have to do more or less the same work. So from MS's perspective the benefit of working around the buggy behaviour is much more prominent than trying to discipline developers by making users suffer.