Im fairly confident that's at least part of the dominance of this approach in big tech. If the tech companies can't collude with no-hire agreements (as they have in the past) to prevent developers from jumping ship to seek raises (i.e. introducing direct anticompetitive barriers) they can collude on an unspoken agreement to raising the barrier to entry, making the labor market less mobile and therefore, artificially decreasing competition. It would be pretty difficult at this point to make a case that the current hiring trends are intentionally colluded anticompetitive labor market practices but the end result is the same.

I say part of the reason because the mess that is the current hiring process is really a multifaceted win approach for big tech and loss approach for most of the labor force.

I suspect if you had a large movement of mid-senior level developers that wanted to shift positions at the same time and began refusing businesses participating in this practice, the industry might be forced to make reasonable changes.

The issue is that our industry has no labor organization and the probability of a critical mass of labor independently making such a fundamental shift (especially in the current economic client) is near zero.