Thanks for your thoughts Osman.
I agree that if you are willing to deal with complexity, volatility, and uncertainty — if you are willing to take on the task of speculation — then Spot instances can be more beneficial. This is also the reason there are so many startups that try to speculate on Spot instances on your behalf.
Google’s strategy is to remove complexity and volatility. To close the loop on the market analogy — dealing with Spot instances is akin to being a professional day-trader, so there are startups that help you manage the process. Google gives you an index fund. Returns may be lower, but risk is significantly lower, and so is volatility.