Unpack grit and you're left with psychological traits which many normal people have.
And also a lot of people with "grit" don't amount to anything. They lack networks, capital or the right idea. Or they have something else that they feel is more important than building a startup: a family, work flexibility, or a hobby that consumes them.
Statistically speaking, poorer people can't afford to undertake the same risks, so they can't take advantage of the same opportunities. Once you hit zero, you can't gamble your way back.
Also, immigrants usually do not carry cultural dead weight - once again I refer to Germany. Starting a company is not really popular here, as you will be socially shunned if you fail (even if you not end up bankrupt in the process, but that's another can of worms). Germans are risk-averse to the extreme, immigrants usually not.
Since I'm also German, I would like offer a different reason. I frequently observe people on HN talking about their "side projects", where they build a simple app or website in their spare time, and people are willing to pay a dollar a month or so, which (when summed over maybe 1000 users) makes for a decent secondary income.
When I consider such a model for myself (just as exploratory thought because I don't have a nice side project idea ATM) it quickly devolves into a nightmare where I spend all my free time filling out tax report forms so that the Finanzamt can collect taxes on my maybe 100 euros per month.
Maybe that's a misconception and it's much easier to operate a side business as a one-man show, but that's the mental image in my head, and that's also the main reason why I would be quite reluctant to even consider just a side project.
Most of the people from poor countries I've known in NZ had domestic help and owned property back home.
-trust funds - no
-expensive educations - university, but it's subsidized here so it's cheap. Almost anyone who can use a uni education can get one in western nations now.
-the disposable income and lack of financial responsibilities to be able to work for free for extended periods of time - I earned this working at a corp job and saving 30% of my income for about four years
-friends in industry - no
-investor class connections - no
-shitload of luck - hard to say. Probably yes.
You don't need the above; internal qualities beat these externals every time.
Countless trust fund babies have tried to start companies and done nothing but fritter away Daddy's money.
Anyway entrepreneurship isn't really about tech giants. Most entrepreneurs aren't starting giant tech corporations. They're just normal people trying to start a lawn care company, a plumbing outfit, a local chicken restaurant chain, a barber shop, etc etc. These kinds of businesses actually do have strong growth potential if targeted and run well. It's just that very few of their proprietors have the business acumen or desire to do it. I can name several always-packed local businesses in my town that could grow quite easily, but they just... don't.
The only time one would endeavor to run a massive business rather than a small one is if you invented/patented something or provided a service that can be scaled and you need help to bootstrap it... in which case unless BillG or DonaldT is yer uncle, you're gonna be sucking on some VC's titty anyway... i. e. they own you.