401k became a thing in part because of deep structural problems with employee pensions. Pensions don't "guarantee" anything in practice and many people lost them or had steep cuts. It is a promise, not a law of physics. 401k/IRA wasn't created for no reason. Pensions are exposed to much more idiosyncratic risk than a 401k and companies are poorly positioned to manage those risks.

Some people might not want to take responsibility for retirement savings in the same way they might not want to take responsibility for providing themselves housing but the alternative is strictly worse.

The only pensions that kind of work is government pensions because they can paper over the structural deficiencies with taxation. But even that has significant limitations as we've seen.

A 401k isn't required to be invested in the stock market. It is advisable but not required.