Senior devs create senior devs - I think it's been this way for a long time. The best people self-select to learn more, work harder, get promoted, and lead teams/projects.
Not everyone wants to become a manager, though.
To get anywhere beyond senior engineer you'll need to be able to explain and convince people that your idea is solid. The best way to learn these skills is to mentor and interact with junior engineers.
The further you go beyond senior engineer, the wider the audience, but you start developing the skills at the 1-1 level.
What does this even mean?
Seniors get more and more expensive until the work gets offshored or companies give in and hire less experienced.
Personal development and self (re)search is what makes 'senior' developers along with certain amount of confidence. The latter can be made via faking, though.