Why do you say that? It is clear that money can be made investing with less than an 8-figure sum. For instance, the Vanguard S&P500 index fund returned 22% last year and 10.66% since its introduction in 1976. The fund minimum is $3,000.
Yes, money "can" clearly be made investing, if you time the market and are lucky. I am disputing the idea that stocks will always generally go up. I think this used to be true but may have changed. Much like "housing prices always go up", which was shown to be absurd.