To say that each of the 40 companies will be worth at least 1 billion is indeed unlikely.
But all that is required for the investors to be "rational" is for the total value of all 40 companies to exceed 40 billion.
So if two companies end up worth 25 billion each and the rest are worthless, that'll still have made it all worthwhile (assuming as an investor you diversified across all 40 companies).
In this scenario, we could rationally say that "each of the 40 companies had a 5% chance (2 out of 40) of being worth 25 billion dollars, which made them worth 25/20 = 1.25 billion dollars each".
But that is not what a common dictionary reading of "40 companies all with a valuation of over 1billion" means.
Yes, that is how a sophisticated investor (who has all 40 companies in their portfolio) will see it.
It is not what a layperson will read - and that is likely to be a problem - jargon should not conflict with natural interpretation, it should complement it.
But all that is required for the investors to be "rational" is for the total value of all 40 companies to exceed 40 billion.
So if two companies end up worth 25 billion each and the rest are worthless, that'll still have made it all worthwhile (assuming as an investor you diversified across all 40 companies).
In this scenario, we could rationally say that "each of the 40 companies had a 5% chance (2 out of 40) of being worth 25 billion dollars, which made them worth 25/20 = 1.25 billion dollars each".