During the boom the last few years, people left after a year or 18 months. Only one stayed a full 2 years largely because he wasn't that great. Honestly can't be bothered any more.
This is an interesting point. For better or worse, the people in the tech world aren't "loyal", and salaries are so crazy they are often looking to leverage their experience into a new position as soon as possible. How do you train people up if you're nothing but a feeder trough for bigger companies?
We shouldn’t be surprised when people fly the nest, and for what it’s worth this happens at even the best companies - people leave to start their own businesses.
What we can do is aim to have them do the best work can, build a good rep for our team, and (selfishly) invest in a strong personal relationship with them so that in 10 years maybe they look back and pay back the favor.
Is loyalty to any employer so utterly and completely dead that I need to enter my future employer-employee relationships with different expectations about loyalty after 1/2/4/5 years?
I'm incredibly fortunate to have lucked out at a place that was acquired 2 weeks after I was let go for being in a similar place as you can imagine when someone spends 4 years somewhere without a promotion or any material recognition of that loyalty. So my 4 years was worth something - at least the after-tax value of my exercised and liquidated stock options.
But that's an incredibly risky basis for value gained by staying somewhere vs. value gained by going somewhere else.
And yes - the reality is that companies are non-fungible and every company will have different values, levels of team talent, investment in their team. Taking the same approach to every company you join, i.e. not going in with a goal/plan in mind, is how you get the average/median outcome for everyone at that company. And you should be going in eyes wide open knowing what that outcome is for every company regardless of which approach you take.
It's the same question of why isn't every restaurant great? Why isn't every haircutter great? By definition, that's impossible - some will always be better than others and the goalposts shift.
So why would anyone hire junior developers than?
If you're not at a company that supports those goals...that's a different topic entirely.
My experience looking at contract work is "yeah, I'm not really interested in being my own benefits manager unless you're willing to pay me $25/hr more to do that work in addition to my regular job".
I'm not really sure why you felt the urge to say this, but perhaps you should be aware that "contractor" status contrasts with "full-time employee" status, not with "at will employment".
At-will specifies who can terminate the contract and on what grounds. It's not relevant to the contractor / FTE distinction.
A huge penalty for leaving the firm that trained you (within a certain time period) is already the norm in other areas. It's also the entire concept of vesting.
Between two years and zero days, there's an awful lot of room to adjust a training period.