I know I have to do research to support this claim, but my understanding is that Google and Meta don’t sell data. They sell access to advertising based on data, but they’re not giving the information away. Much of that information is stuff that doesn’t change frequently, so once you sell it there’s no reason to come back for more. The data is their competitive advantage and they have the ad business to support it. For smaller companies or ones that don’t have this turbo-charge ad business, they do sell data because they don’t have an ad network to add value on top of the data they collect, so the most they can do is just sell it.
From that perspective, compartmentalizing the services you use (when it comes to the Big Tech companies) does make sense. Why have duplicates of your data shared between Google and Microsoft for example if you can totally get by with only one of them?
Like others have shared, most folks on this forum graduate away from Big Tech, but the mentality of trust one or a few companies to handle as much for you as possible is still there. Proton and the ecosystem they’re trying to build is proof of that market.
Why choose one approach over another? To me, it depends on how advanced your threat model is and how willing you are to be your own IT department. If there’s only so much you can do or have the mental bandwidth for, you will gravitate to the easier to adopt solutions. If you want to go further, you benefit by spreading out among services.