Growth mindset is hard to achieve. Humans tend to look for comfort and stick with it until something happens. No one really wants to get out of their comfort zones until they are forced by an event or a difficult situation. Rarely have I ever encountered a person who wants to change something and actually do something about it, though it is still possible with the right approach and the right support.
Franky1 mentioned career paths and it is one of the prime examples of this. We tend to specialize in something until it occurs to us that we no longer want it or there are other high-paying jobs that we 'might' get a liking to. Economic conditions force people to change jobs and grow, but if the economy is good and our salaries still fulfill our expenses, I guess no one will have to hop jobs and companies every now and then.
The difference between a fixed mindset and a growth mindset is that a fixed mindset means that they always enjoy the current situation without acting on new things and don't care about any innovations so they are always in a safe condition even if there is a downturn, often they consider themselves unable to do things beyond his abilities. whereas those with a growth mindset always look for new challenges in life as long as it brings positive things to themselves, they see that whatever failures will one day bring change to themselves, if they hear and see other people succeed they continue to find out and ask for experience and how to be successful like that person
Keeping our mind ready for growth is the best while we shun the ugly mindset of fixation (if it is toward stagnancy), but at times, it depends on the definition of the two as even a fixed mindset could be very good in another school of thought, but I will not go there as I like to stick to the ideology of the OP right now. Based on the OP's ideology which you also rely on in your reply, I believe that many people are too comfortable with their situation, they do not want to wake up and move forward. Some are so dull in reasoning and creativity while others are too lazy to do anything that will move them forward, they are just relaxed or continue to procrastinate as if the time is waiting for anybody.
Many do not want to learn and expose themselves to ideas that can shape their lives positively, this will always keep them in the same sport whether they are poor or average. This is the kind of people that will always complain rather than take steps to better themselves and many would not even believe that they need more income stream but rather depend on a single source of income even as they are having financial challenges. It is often late before they realise this, while others will never realise it and will remain poor or not have that significant advancement for the rest of their life.