Comment by WhompingWindows

Juniors are beginners, learners, apprentices, and are bound to make mistakes and design things poorly. The issue is there are so few high-quality engineers relative to the demand, and it's hard to prove who is high-quality before they're onboard for a few months. So, if someone is high-quality, you really don't want to lose them, so you promote them, pay them more, try your best to keep them on-board. There's a benefit to elevating them out of the weeds, because often they can glance at the weeds and tell someone else how to clean it up easily, without spending their effort to actually do it.

Furthermore, they can glance at 10 patches of weeds, 10 junior engineers, and find the couple that need more guidance than the others. They can leverage their knowledge through others, assessing their strengths/weaknesses as coders in ways juniors never could.