When nobody is going to work for the same company for decades what is the point? This is both management's fault for not valuing the people they have (it is very common for cost of living raises to not match inflation or much less increased value as people get better), layoffs; but also workers for looking for a new job (only partially because of the above) when they have one.

I think in the ideal world 30-60% of the people who retire from your company should have started there just out of school. Much less than that and you don't get the value of experience built up over time. Much more and you miss out of good ideas others are doing. However there are many ways the world will never be ideal...