Being booked out 2-5 months ahead is typical for us. Two weeks is effectively zero notice period because you'll almost always have more remaining days of paid time off than that. If we had to account for N people being able to leave effectively on the spot, we'd not be able to sell more than 8-N persons concurrently (we're a small team), at least not more than a few days ahead. At N=1 person, that's already 13% lower turnover for the whole company.
After the trial/probation period where this notice period is not in effect, when I know what the employment is like, I'd much rather get a 13% higher salary and, should I choose to quit, wrap things up properly and do the job for 2-3 more months. (The notice period is not as long as we schedule ahead for: with 2 months' notice, we can find a good freelancer and get the paperwork done without time pressure, or the client can still find another firm in the worst case.)
Since I was fine with doing this job for years now, those months seem insignificant for the benefits that go both ways.
Laws permitting--and I assume any extended notice period would be/should be mutual--companies can put any appropriate terms in their employment contracts. But it's certainly not the norm in the US. I'd expect most common would be two weeks notice and you get paid out for any unused paid time off.
For most people, multiple months notice wouldn't work well. Either you quit without an offer in hand and spend half your remaining time job hunting or you have an offer but your potential new employer won't wait more than a month. I'd certainly think very hard before entering into such an arrangement as it would make getting a new job riskier.
After the trial/probation period where this notice period is not in effect, when I know what the employment is like, I'd much rather get a 13% higher salary and, should I choose to quit, wrap things up properly and do the job for 2-3 more months. (The notice period is not as long as we schedule ahead for: with 2 months' notice, we can find a good freelancer and get the paperwork done without time pressure, or the client can still find another firm in the worst case.)
Since I was fine with doing this job for years now, those months seem insignificant for the benefits that go both ways.