Both CloudFlare and Google are for-profit corporations which want to take actions to maximize their profits. Insomuch as they are profit maximizing, we should expect them to take actions where the expected gain is greater than the expected cost, and to prioritize actions which have the maximum gain over actions which are only barely profitable.

If the cost -- in terms of extra labor and reputation if the data-selling becomes public -- is estimated to be less than people are willing to pay for the data, why would any profit-seeking corporation choose not to sell your data?

We can't trust companies not to sell poisoned food, even though that's a huge reputational hit. We can't trust companies manufacturing herbal, vitamin or nutritional supplements to actually put the herb, vitamin or nutritional factor they claim they are in the bottles they sell. We can't trust the makers of USB cables to produce cables that actually meet the USB specifications. Why should we believe that any corporation, regardless of whether or not you pay them for their goods and services, would leave the money to be made selling your data on the table, even if there's a potential reputational hit if the practice becomes public?