That's for common ideas. "Let's make a Facebook for dogs", "dollar shave club", etc. But those are not patentable in the first place (and if they are in some country, they shouldn't be).
Here we are talking for invention ideas. Which are not plenty, and which often require not just insight that billions couldn't manage to have (the invention of the carriage wheel -- which the pro-Columbian population of the Americas managed to miss, even though they had wheel shaped items for other uses), but also millions in R&D (e.g. to design. build, make efficient to mass produce and test a new kind of plane engine or a more efficient battery).
In a lot of those cases where the invention scratches an itch there's very little "correct productization" needed. If you make a better battery material for example, you just sell it like everybody else sells batteries (plus some marketing for its longer life). Some things literally sell themselves.