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.