To maximize the effectiveness of a software development organization, you need to keep people for more than a few years, so they can absorb institutional knowledge and keep it from being lost. If only your senior devs know how the system works, you're in dire straits because they'll have a bad day and leave. Or you'll have too many of them and big egos will clash. (Not to mention, senior devs do not have "beginner mindset" and often miss the forest for the trees). Or at the very least your payroll will be larger than it needs to be, paying for all those seniors. Ideally, you want to hire junior developers, and in-parallel, level up both their dev skills and institutional knowledge.

This isn't exactly rocket science, and I'm pretty sure software development leaders have known this for 4+ decades, but for some reason the current crop of leaders don't "get" software. I think a lot of wisdom was destroyed in the dot-com bubble crash, and the survivors, or the ones that grew up in the rubble (Google, Amazon, Netflix, Facebook, Github) were the only ones who maintained these principles. Everyone else got a generic MBA running the show.