you're still paying interest on borrowed money. Why not just drop the cash and put what you saved on interest into investments?
Why use your money at it's peak value when you can use someone else's money that's depreciating?
So, for example, $10k today is going to be worth slightly more than $10k tomorrow; it'll be worth even less the next day and so on. If I drop $10k on a car, that's $10k worth of today's dollars that I don't have to put into my IRA or other investments.
If I borrow $10k I pay you (for example) $200 in today's dollars and invest the other $9800. Then next month, I give you another $200 dollars, but that $200 is worth a bit less than it was last month. Yes, there's interest built into that payment, but if my annual interest rate is 1.75% and inflation is at 2.0%, then the amount of money I save each month by financing is going to be 200(.02/12) - 200(.0175/12) or a difference of about $0.04 per month. You're actually
saving money by financing. Granted, it's really not much at all, but still better than paying cash, especially when...
...you look at the value of your sunk cost. You've dropped $10k on a depreciating asset, so your $10k is worth even less with each use of the car, whilst the money you invest can be earning whatever the market yields.
Plus you get to drive a nicer car.