Prioritisation is hard. One reason why it’s hard is that starting new things is always more attractive than stopping old ones. There are all sorts of reasons for that – many nicely set out in this post – which include the ease with which we overlook the opportunity cost: if we start this new thing, what do we no longer have the capacity or attention span to do? That of course is a problem for the organisation as a whole, not for the proponents of the new shiny thing, so it all too easily becomes one which is brushed aside, because there isn’t anybody whose job is to address it.
There is a closely related problem, pithily described, it appears, by Kurt Vonnegut:
Another flaw in the human character is that everybody wants to build and nobody wants to do maintenance.
That can have consequences from the irritatingly inefficient to the utterly terrifying, but all contributing to the wider problem, that the more change there is going on, the more likely it is that the changes will collide with each other unproductively, and the more it becomes important to understand and manage the dependencies and interactions between projects, as much as to understand and manage each of the contributing initiatives.