Disclaimer: this is from the perspective of someone who is NOT a Senior engineer. My experience so far has been that there is very little work in a large organ

Disclaimer: this is from the perspective of someone who is NOT a Senior engineer. 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.