A person in the US founding a startup has access and exposure to the deepest capital markets in the world, the largest domestic market in the world, a stable legal and political environment, and a phenomenal talent pool. A person doing the same in e.g. Vietnam has access to almost 0 VC funding, tiny domestic market, his efforts are hindered by a capricious and restrictive legal and political environment and a very low skilled talent pool. Someone with the same competency as say Bill Gates has an infinitely lower chance of making it big.

People do not risk their lives and leave their families behind because they really love going to Cheesecake Factory everday in the US, it's because opportunities often flat out do not exist in their country for what they want to do.

Even among successful businesses founded in (currently or formerly) less industrialized countries, you will see that a huge proportion are actually state owned or backed (e.g. TSMC, Samsung)

Opportunities didn't exist in America until Americans made them exist.

Apple was founded in a garage.

Time for people in other countries to do the same for their own country.

A good product or a good idea will surface.

Your excuses fall on deaf ears.

America had been a pristine land of opportunity long before the first American was born. Americans didn't make America, America made Americans.

Apple was founded after WWII (it would not exist today without a WWII victory).

Time for people in other countries to do the same what? War? More natives killing?

A good product or a good idea will surface tomorrow eventually.

But men being men will go where the money/food is today, no excuses needed. In fact no killing of natives needed either, so what's holding you back really?

...and yet America was built by immigrants who couldn't make opportunities at home.

America was a colony who overthrew a repressive dictatorship for it's independence.

...made up of immigrants who were looking for a better life.

They literally founded the country.