I think a lot of people don't change job because looking for another job involve all kind of stress. Am I taking the right decision? Will I be happier at the new position? What if I join and that company is announcing 1 year from now that it will have to layoff workers? Also some hiring process are so bureaucratic and long these days that just the thought of enduring all of it is tiring. Also when you are reaching 45y old you are thinking probably more conservatively.

I am saying this having moved jobs 6 times in 23 years.