To the inventor? Perhaps, but there is a great deal of risk and additional work involved. Most inventors take the easy route rather than trying to market and sell their inventions themselves. However, there is a lot of risk involved in doing so. Risk that your idea won't actually translate into a workable invention. Business risk, and so on. With an easy payday in sight there is a greater incentive for people to spend their spare time working on such things, if they have domain expertise. In contrast, working on their own they'd have to contend with the risk that their invention won't actually have as much of a market as they thought or that they wouldn't be able to monetize it very effectively, and so on. With a prize a lot of that risk becomes less important, and shifted onto google's plate instead of the inventor's.
Also, google isn't necessarily depriving the inventor of patent/licensing rights, the $1M dollar prize is likely just the beginning of monetary return for the invention.
It reminds me of that show Silicon Valley where the Hooli (Google) guy offers him $10m for his algorithm, but he decides to go it alone for the chance of big bucks.