My experience so far has been that there is very little work in a large organization that doesn't affect multiple teams at some point.
So if you're a Senior+ engineer building a complex system, it's highly likely to impact a lot of other people in the company. Building something like that without getting impacted teams onboard with the idea seems like a recipe for organizational strife.
Another thing that comes to mind is organizational goals. If the company has high level goals they want to achieve, having people (Esp very Senior people) working on multiple things unrelated to those goals doesn't seem conducive to success.
Also, the more senior you are the more visible you tend to be. So what you work on is probably going to be noticed more. I know that I would find it weird if I found out a Staff or Senior Staff engineer was off working on random things instead of leading an important project.
I definitely think Senior+ people should have some freedom, but absolute freedom doesn't seem like a good idea for anyone. When you're at a certain level what you do affects way more people than just yourself. Titles have a lot of weight to other people.
There is no reason you can just have one or the other, if you already have a lot of tight collaboration then you probably miss out on many potential changes that are too disruptive to be politically feasible. But you are right that you can't have only individual work, organizations needs tightly collaborating teams to be an organization.
Why? As long as what they do doesn't interfere with others work why does it matter if they don't communicate everything immediately, rather than at a meeting at a later date? If they don't deliver anything useful you put them on a PIP and ultimately fire them, just like everybody else, I don't really see what changes here.