[graysnorf]

This is an excellent point, and perhaps an argument against at-will employment. Even if you had a candidate who was willing to commit to staying employed long enough to justify the time and expense of their training, in many US States they lack the legal power to agree to such a contract.

Extrapolating from personal experience here as a programmer but it looks tough for a couple of reasons, one of which is pay. Employers tend to give very good starting salaries for experienced people, and very poor raises. So employees sign up inexperienced at low pay, get trained and get raises that put them below market rates, so their incentives tell them to do exactly the job hopping you describe.

[mhurron]

Being in an at-will state does not remove the ability to have and enforce an employment contract.