If you look at software of that era, he wasn't doing something nobody else could do. They had a BASIC interpreter, but it wasn't the first or notably better. MS-DOS certainly worked, but it was at least heavily inspired by CP/M even if the plagiarism accusations were wrong. Being a capable programmer was necessary to his success but it was far from the reason: there were many others around, and they did well but the legendary wealth came to the person whose mother was on IBM's board when he made that company-defining sale. He subsequently executed well but again not uniquely so — anyone who used Microsoft software of that era could tell you that it wasn't the quality of that software which kept people using it. He executed well, and certainly wasn’t shy about an … aggressive … legal strategy but there was also a substantial portion of nepotism and luck.
The world has many people who were smart and hardworking but will never be close to that level of success because they didn’t have the family connections, startups capitol, friends they made at the right school, or the freedom to make a big gamble.
If so, what you're missing is that Gates knew how to play "the game." He knew how to close sales, how to navigate the muddy waters of business, and how to leverage success into more success.
> If "having a rich father" is the only thing that matters, why isn't everyone with a rich father a billionaire?
My position is that there are multiple factors and neither is sufficient on their own.
I think Bill Gates, Elon Musk are all examples of great success. It doesn't mean they are vastly different from the similar hard working people in their fields. It just means that they did a "little" more combined with lots of other factors that put them where they are.
That matters personally because you want to set realistic expectations: if you can’t afford to write off a couple of year’s work, launching a startup probably isn’t the best call for you compared to a more staid job which means you don’t need to worry about rent money or health insurance.
It also matters societally because these guys really want to influence our laws, educational system, tax code, etc. and that context is critical. If a billionaire says we should cut taxes on startups to help people climb the ladder, the first question should be how much of the money will go to rich kids from Ivy League schools versus the ones featured in the ad. Similarly, if they’re pushing kids to drop out of college for startups or turning public schools into coding camp, we should be asking how that’ll work out for everyone: the prospects for a kid with affluent high-status parents and a robust social network are quite different from kids who are poor, brown, in the wrong part of the country, etc. and such a policy might be especially dubious if it meant that they have lower negotiating power to get better jobs at the companies run by people making such suggestions.