It's not just about the $500k, it's about the freedom to do your project your way from start to finish. I can't get $500k from any investors to do my work; their number one question is what's their ROI, which is not even in the universe of my concerns. The last thing I ever want to think about is how to profit from my research.
Another choice is to join a company and then convince that company my idea is worth while. If I get the greenlight to go ahead that's great, but then I'm still always living under the threat of being fired or the project getting canned. Any University is happy to have a CAREER recipient, and your award is portable between institutions.
And sure you'd possibly be able to convince your company to sponsor a project you're interested in leading, but the for something like $500k you'd better have a good business case for it, and I can't imagine them approving something that would last 5 years unless it really aligns with their business goals. In order to get the clout to actually ask for this kind of project you'd also need to be at the company for a while, whereas something like a CAREER award is intended for early-career faculty. Imagine going up to your boss and saying: "You know that job you hired me for? I'd like you to keep paying me my regular salary, but I'd also like $500k to work on my own pet project about 70% of the time from September to May, and 100% over the summer. Oh, and I'd like to do this for the next 5 years."