I have a bunch of issues with the "Privacy Sandbox", but my #1 issue is that it's called "Privacy Sandbox". That term implies that a sandbox is being used to preserve your privacy, when it is, in fact, a system designed for the opposite of that.
What's holding everyone back? I understand that without users there won't be apps, but also without apps there won't be users, since they offer just the basics.
Imagine if TikTok or WhatsApp have had an app for those others OSes
Heck, you can just use lineage os without the Google services to get a taste of this. And that's a system where you still can get all the Apps with a tiny bit of effort, as long as they don't depend on the Google services. It sucks for the most part.
But really, since you asked, just try it. Get some used phone that's supported by lineage OS and challenge yourself to use it exclusively for a month. Or maybe for fun/hard mode, get a Lumia 950 and try that for a month.
A surprising and hilarious number of things, including some of Google's own apps, show "X won't work unless you enable Google Play Services" popups and then continue working just fine. (I'm guessing they link against some client library that shows that on all function calls, but then doesn't throw an exception.)
Its possible to add Android auto stubs to it to give privileged access, compile your own build, sign it, flash it, and install the apks yourself as a DIY middle ground. I did it for a pixel 6 and was happy with it but bootlooped the phone applying my first compiled OTA update so this scared me off trying it again and I went back to stock. I understand why the team is against it but unfortunate.
Maybe another take on your question is why did windows phone and bbm fail?
One such example is CalyxOS. Using it right now. It comes with both F-Droid and Aurora Store. The latter let's you download anonymously from the playstore.
Just yesterday I actually had time to read that new Apple "Privacy" Statement that pops up on a Mac for some reason since a few weeks and they put a blunt lie on top about how "private" their service is and just a few lines later they tell you that they grab actually all your private data.
Every EU website now pops up a "privacy statement" where they actually tell you that they DO NOT respect your privacy.
I am sure there is a technical term for that, I would simply describe it as "producing cognitive dissonance in the most obvious way and make it look fine".
It took already an enormous effort to get all these companies to actually have to report about their abuse of your private data, in EU even make users agree.
However, it did not change anything - most companies still break your privacy even with more fun doing it, as you agreed.
A terrible and wasteful development of modern primitive capitalism.
And what do you mean "lying" ? There are no lies anymore. Only "sources", CIA press releases and "insert your enemy here" propaganda. /s
"Always dispose of the difficult bit in the title. Does less harm there than in the text." https://www.youtube.com/watch?v=40Br165MhLU