They did plenty of due diligence to protect their own interests.
Their term sheets gave them a big chunk of the "limited supply" tokens. So even if the business model was trash, they could cash out well before the market for that coin collapsed.
It is similar to when investment banks underwrite stock issues; they purchase a chunk of the stock directly from the company at an agreed-upon price. The company gets guaranteed funds, and the bank is free to sell the shares on a secondary market and potentially pick up a profit.
What's missing in crypto are the safeguards that ensure that banks + companies do not collude on pump and dumps in the securities markets. These include quarterly financial audits and oversight from a watchdog agency like the SEC. Obviously they are far from perfect, but considering the anti-regulation nature of US business (even after the Great Depression), the fact they even exist is a small triumph.