These are standard contracts in many places of the world with stronger labor laws than the US.

It does not mean you have tenure, or any non sense like that. It means there are specific, objective causes to terminate your contract, which include but may not be limited to: gross incompetence, contempt for workplace discipline, frequent absenteeism, criminal/delinquent activity against or otherwise involving company assets, etc.

If the employer cannot or will not prove this kind of behaviors from the part of the employee, he still can terminate the contract, but there's a minimal severance mandated by law, which depends both on current monthly salary and on seniority.[1]

i.e In my country, you are supposed to get 3 months salary, plus 20 days per each full year you held the position. Some employers will still low ball you if they think they can get away with it, but they will still give you more than what you'd get after suing and paying the lawyer's commission.

If you don't understand this, put yourself in the shoes of someone who has to work for a living. Is the flexibility to change jobs at will worth a 30% chance of being out of work for 2 years when you get laid off during a bust (when no one else is hiring either)? Most people would say no. The reality, one that more people are accepting these days, is that every employer offers pretty much the same work environment and pay, whether a product of collusion or parallel evolution. Ceteris paribus, as it usually is, security is a perk.

As a more concrete answer to your question, professional athletes do it all the time. The elite among them get the longest-term contracts, and actively push for them. There are other jobs as well that involve guaranteed terms, many of which don't have the unique attributes (limited prime years, injury risks) associated with being an athlete. Those same athletes' coaches, for example. Actors. Corporate-to-corporate contracts often have minimum terms and guaranteed spend, too.

Why would the company offer such terms? I think the OP covered that pretty well. Turnover is expensive.

CEOs sign agreements like this regularly - well, maybe structured a bit differently. The company doesn't want the CEO to leave shorter than some nominal time - so some portion of the compensation is structured to mature over time. The CEO doesn't want some uncontrollable market or political shift to put him out of work (with some reputation cost), so some compensation for early separation is negotiated.

Employees generally don't get that kind of consideration - especially in established companies. Companies used to have incentives such as pensions that were a generally applicable, long-term retention incentive. However, the market decided that carrying that type of long-term obligation wasn't desirable for companies. In some ways workers benefited too by lowering of their employment switching costs and not carrying the risk that a company doesn't survive or honor those obligations.

To me, that's sort of the point – you can understand why it's hard to keep employees for N years by thinking about what the terms of an N-year contract would have to look like, and whether anyone would sign it.