Also, in my experience, people are already doing the thing before they get promoted to it. There's a continuum of skills. From developer to senior developer, you're not just one day developer with your heads down or writing code and the next day you're only architecting and mentoring others. You start out as a developer and if you're good at mentoring, people start to seek you out for questions and soon you become the mentor and you get promoted because you're already doing it in a small level and they want to reward you and encourage that. Similar for architecting the system, if you're a low level developer and thinking about architecture things you're already doing that work and you're reward it for it by giving more responsibility to do it more.

However, one thing to note is the senior level positions, the higher you go, the more you're a people person. A low-level developer can think about architecture all day long, but because they never talk to anyone about the ideas, discuss if it's really good or bad, understand the pros and cons of the ideas that others have, they're going to remain a low-level developer. This is why senior developers move in and out of management very often in a lot of companies. The jobs are not nearly as different as people would imagine. In both cases, you're more a people person than a technical person. It's just that as the senior developer, you still keep that developer hat on and write code, whereas as a manager, you're only a people person.