Unfortunately, from my perspective - the people who step into those management roles far too often are even worse than an empty seat.
Very hard to hire for, unfortantely, much harder than most (but not all; software architecture for example will either make or break your project, but you'll only really know in 12-36 months what will be the case) individual contributors. because all the work is very squish, with uncertain outcomes, and can often only be accurately assessed in aggregate and a postierori. Even at a relatively low level.
Consider someone responsible for a team delivering a Thing by a certain date, which is a responsibility that companies might put on either line or project management. The Thing looks like it might be late based on aggregate indicators, but based on quality indicators and the nature of the work already done vs. still open it might also either fit just fine, or at least be in reasonable quality with further work being done after release.
Do you do the save thing and go to your stakeholders and tell you that Thing will or might be late? What are the organizational costs of a delay that will be unnecessary, or a delay that turns out to be unnecessary? How do you feel about the possibility of a 'reasonable quality' initial release, and cost of rework/vs gain of market entry as planned? ...
Those are all judgment calls where the person making them can only be assessed for a posteriori and in aggregate, because if you move ahead after a single judgement call that didn't work out you will get what you don't want: A culture where no one will take responsibility, either outright or by counterproductive behaviour of not only including some buffers but enough buffers to stack them to Mars and back.
(Agile doesn't really help you avoid those judgement calls either; what it can do is to help you to lower the stakes of those calls, and make them with a better information basis, and give you more decision points.)
The higher up the stack it goes the less squishy it becomes, because both your information basis and your means of influencing outcomes become more diffuse and less direct.