One of the benefits of cloud is aggregated signals.

It's possible to do calculations horizontally across everyone's data to produce distilled signals (e.g. rankings or recommendation) that benefit everyone.

Those distilled signals are more than the sum of its parts; every user benefits from everyone pooling their data into the calculation.

But in today's physics of trust, the only way to accomplish this is for one entity to have all of the data in plaintext.

You then have to trust that one entity to be a good-faith actor with the data and not use it in ways not aligned with your incentives.

That's a bad assumption today, where the aggregators have gargantuan Terms of Service that reserve the right for them to do just about anything they can think of with your data, and also have incentives not aligned with yours.

In addition, that one entity likely won't give the contributors of that data the distilled result, since it's the aggregator's proprietary signal.

People would be happy to contribute their incidental data for free, if no other entity had access to it and they were able to get access to the distilled signals.

If they knew their data couldn't be used in any identifying way, they wouldn't even need to collectively own the distilled signal, just have access to it.