More specifically, some folks like to teach because it makes them feel like an expert when they're not. That's bad.
Some folks like to teach because it helps them learn-by-teaching and helps their pupils learn-by-questioning (and learn by questioning and receiving an honest "no idea/I might be wrong!").
The quantity that's in short supply is not expertise. It's humility.
> In practice it is more complex - people with a talent for teaching and leadership and are experts are incredibly rare.
Not in my experience. While there are obviously fewer people who have both traits, they're not at all rare. In practice, what I see is that such people shift away from teaching/mentoring as it takes time/effort that their manager does not reward.
If you want talented people who mentor well, make sure such mentoring is rewarded.
> what I see is that such people shift away from teaching/mentoring as it takes time/effort that their manager does not reward
I don’t think it’s that simple. I work with tons of talented engineers who put a huge amount of effort into tasks that management doesn’t care about - like refactoring our codebase.
In contrast everywhere I have worked management has cared about being able to level up new developers and under performers (assuming it’s a skill deficit).
To add to this one of the most soul crushing tasks I’ve had to do is to manage out good people who are under performing.
If I could say “BeetleB, I’m pairing you with Joe for the next 6 months - I don’t care if your output halves but I need you to bring him up to speed or we have to let him go” and you could train him up - well you would be worth your weight in gold.
In practice it is more complex - people with a talent for teaching and leadership and are experts are incredibly rare.
What we often end up with is a mediocre dev taking on the teaching role and helping build a mediocre team.