> Cash windfalls can absolutely build wealth.

Yes, but that's facile.

Do they, commonly? No.

> Also 100k invested in the market will yield you probably around 7k, which is a lot, especially you don't touch it and let it compound.

You came so close to getting the point, and then kept walking with your own predetermined idea! "Why don't these single-income, struggling mothers and unemployed homeless people just take this cash and invest it?" is the most privilege-laden, oblivious idea I've heard in a while.