if surveillance capitalism was so successful, you would expect the overall ad spending to have spiked recently , since people claim to have found the holy grail that turns ads directly into profits. But it hasn't.
And they can sell information to your insurance company etc. It doesn't have to be only about targetting you with ads. Information about you can be valuable in other ways.
And it doesn't even have to be useful to the companies although it certainly helps. They just need to /think/ it is useful to sell it. Theranos raked in lots of money before it was revealed to be a lie.
Capitalism and values are fundamentally a means of resource allocation - if everyone is wrong about what really matters that means it is valued even if its true utility is nill or negative.