Worse, many firms are put off by juniors for entirely preventable reasons. In their minds, juniors are undesirable because the moment they are trained up, they tend to jump ship for senior positions elsewhere. Why train your competition, right?
The reason they jump ship is because the firm refuses to re-evaluate them for what they are worth, and keeps them on work meant to free up the company's existing senior staff (i.e., dead-end grunt-work that results in burnout). If you, as a junior developer, want to be re-valued, you need to jump ship.
This creates a feedback loop. Companies view juniors as a cheaper developer you _might_ get 2 years of low-cost work out of (after training) before they'll leave, creating a self fulfilling prophecy.
I've watched (and experienced) this loop multiple times. It's utterly baffling how firms would rather go through the cost and drain of finding and replacing talent rather than re-evaluate and pay their existing, proven talent what they are worth on the open market.
Workers would rather not move around. Workers would rather have a stable position in a job they like, in a community where they can purchase a home and build lives and/or families. Once you get past 35, playing the required musical-chairs needed to advance your career is a real drag. It does not need to be this way.
I really disagree. These junior engineers you're talking about are mostly in their early 20's (even if they're older and switching from a different career track, they're by definition new to the industry and still have a lot to learn). In my experience, they definitely do want to move around. And even if there is a great track for internal promotions and the compensation is going to be the same whether they stay or leave, it honestly is usually in their best interest to move around every couple of years anyway early in their career. They'll meet more new people to grow their professional network faster, work on new problems, see different ways of how teams operate and what works better/worse, and gain more experience faster.
I do think that for the very top performers, most companies should probably be much more aggressive than they are. If someone is really crushing it, like in say the top 1-5% of performers, be ridiculously proactive and promote them from junior engineer to Staff Engineer within 18 months or something. I've seen a couple of people over my career that actually were performing at that level, and no external company is going to give them that big of a boost, so it's a good chance to use your inside information to be more competitive. Otherwise, for the majority of folks that are learning/advancing at a more normal pace, I don't think there's really much a company can do to keep them longer. (Not that you shouldn't even try, it's still a continuum and if you do a really bad job at career growth internally you'll lose even more people faster. But you shouldn't expect to be able to keep most people beyond 2-3 years).
Hiring Juniors is a positive externality that the company does not see a penny of. They only see a penny of that externality if they don't give a raise, and that Junior chooses to stick around anyway. You get to exploit that he made friends or is stuck in your part of the city due to a lease or otherwise makes a poor financial decision.
It's interesting that the worse the interview process, the less the Junior will want to go through it, the more the company benefits. You make your process painful so your competitors make their process painful so both of you hold onto your Juniors for more time.
If you can fix the externality problem this goes away, but that's not easy.
I work at a fairly small company that hires juniors. We pay them well, and give them more responsibility in pay as we see them improving.
Most of them still want to move on, usually to change technologies or gain more responsibility even faster.
Sometimes they want to move cities for almost random reasons, and they're willing to just find a new job and do it.
So while I somewhat agree that devs don't want to move jobs, juniors devs often do, and I think they're a lot more likely to move jobs than senior devs.
Honestly, I think having engineers come and go is a net win for companies. I've worked at places where the "old guard" has been around forever and they are inevitably stubborn, obstinate, and convinced there is no other way to solve the problem. By changing jobs and environments, you get to see in practice that there are many different ways to implement a solution. Only seeing one set of systems (unless they are a FAANG, which is large enough to have the breadth to counteract it), would ultimately cause those architectures to stagnate, injecting new blood is also injecting new ideas.
I do however, agree with your sentiment, those junior folks that are getting all the work done only get rewarded with more work to do.
The reason they jump ship is because the firm refuses to re-evaluate them for what they are worth, and keeps them on work meant to free up the company's existing senior staff (i.e., dead-end grunt-work that results in burnout). If you, as a junior developer, want to be re-valued, you need to jump ship.
This creates a feedback loop. Companies view juniors as a cheaper developer you _might_ get 2 years of low-cost work out of (after training) before they'll leave, creating a self fulfilling prophecy.
I've watched (and experienced) this loop multiple times. It's utterly baffling how firms would rather go through the cost and drain of finding and replacing talent rather than re-evaluate and pay their existing, proven talent what they are worth on the open market.
Workers would rather not move around. Workers would rather have a stable position in a job they like, in a community where they can purchase a home and build lives and/or families. Once you get past 35, playing the required musical-chairs needed to advance your career is a real drag. It does not need to be this way.