In my view, there is no such thing as free market capitalism without regulation. The only thing that could create anything resembling a "free market" in the first place is regulation. The whole point of the endeavor is to enact regulations that essentially play whack-a-mole in making every means of profit illegal, except for means that serve the greater good, i.e. producing, serving, innovating, and/or lowering prices, or investing in those that do.

Without regulations (just a fancy word for "laws"), few people would bother to do any of these things. As it would be much more profitable to simply sabotage competitors, form cabals or monopolies, oppress and steal from the populace, conquer and loot your neighbors, lie and deceive and trick your partners, etc. And even if it weren't, anyone who did want to truly innovate or produce something useful would be discouraged by the fact that, due to others engaging in the above activities, they wouldn't see any profit.

So, to answer your question…

> How often does this actually happen?

All the time! Hundreds of thousands of times per year! Because we don't live in an unregulated free market, because there's no such thing and the concept is absurd on its face.

There are plenty of gaps and inefficiencies where new businesses can provide value to customers at scale who will happily part with their money in return.

Not to mention the fact that the constant march of technology (as well as changes in policy, culture, environment, knowledge, etc.) are constantly tearing open new holes in the market.