The qualifications for being a Junior developer are (1) familiarity with new frameworks (2) nimbleness with polyglot approaches (3) ability to code considerably more than sit in meetings (4) an approach towards getting things done, rather than spend time considering getting things done.
Not every developer has the chops to be a Junior developer, but if a Senior developer has the interest and is willing to work hard at it, they can make it.
This is silly. Few places seriously expect a junior developer to be familiar with new frameworks. They expect to get a Java kid fresh out of school. And the fixation on getting things done rather than careful consideration can--and does, I did it as a junior, it's part of becoming not-a-junior--leads to getting the wrong thing done. Spending a week moving mostly sideways is no different than spending a couple days thinking and discussing and a couple days moving mostly forward, except you might make more progress depending on exactly how far the cowboy missed the mark in their haste to just write code, bruv. (And the cowboy will miss. Everyone does, even if you're a genius. Not that groups of developers can't miss, too--but after a while you start to realize that they usually miss much closer.)
The role of junior engineers is that they are teachable and can generate value while they are being taught; the role of senior engineers is that they are teachers while both generating value of their own. There is no rarity to junior developers, there's potential plus inexperience. And that's it.
The qualifications for being a Junior developer are (1) familiarity with new frameworks (2) nimbleness with polyglot approaches (3) ability to code considerably more than sit in meetings (4) an approach towards getting things done, rather than spend time considering getting things done.
Not every developer has the chops to be a Junior developer, but if a Senior developer has the interest and is willing to work hard at it, they can make it.