Its up to the employee to continue to build marketable skills, not the employer. If the employee is content in their position, then that's that.
What happens if you don’t train your employees and they stay?
Why would anyone want a team who hasn’t updated their skillset since 2006? That’s the epitome of the “Dead Sea Effect”
Employees need to take responsibility for their career and growth. I am responsible for continuing my learning and maintaining my skill set. To that end though, I choose to work places that encourage and support that since it's in their own interest.