You can create a company that has ludicrously limited opportunities to return its capital, and sell those to the public. You simply have to comply with the SEC's registration and disclosure rules --- in particular, you have to publish quarterly audited financials confirming your limited prospects.
That is the difference between the "3x leveraged ETF" and the "company that has a chance at profit" in your example, not some weird value judgement the SEC is making.
So some financial products where they will always drift to zero are fine, but investments in companies that have a chance to profit aren't allowed.