Thanks for the clarification.

If indeed it were the case that biomedical research isn't facing a talent-constraint, i.e., they're able to get as many people as they want with these awesome qualifications, then I would agree with you.

But the impression I got is that they aren't able to find "enough" such people (at the low prices they currently offer). Which raises the question of whether there simply don't exist more such people at the margin (that was my explanation 1) or that even if they did find more people, every such person would be willing to work for low pay.

(5) seems more convincing to me, and your elaboration of it makes sense.