It's definitely not for lack of hard work. Not everyone can "make it." That'd be impossible. Making it requires one to achieve a high-end job with good pay. If everyone made it, who would clean toilets, serve burgers, and do all the shitty little jobs that need to be done in society? Why can't the other 90% of the population make it? Because that'd be impossible. Lack of opportunity and education/resources is a big part of it, but many still wouldn't make it because they are simply not smart/skilled/artistic/athletic enough to make it. What we could do is change that split from 90/10 to something more favorable.
I don't think that can happen with a hyperfocus on profits over meeting people's needs. The number one reason that ratio has become this way is the lack of government protection for workers: enforcing proper minimum wages, providing proper time off, healthcare, childcare, housing, and education options. There's plenty more. When people's basic needs (Maslow's hierarchy) aren't met, we shouldn't be surprised that they're not living up to their full potential, or in some cases, any potential at all. That's why most of the other 90% of people can't make it. Their physiological and safety needs (levels 1 and 2 on Maslow's hierarchy) are simply not met.