It's worse than that. Google Photos sends push notifications telling you to buy photo books and prints unless you opt out. Play Books also sends push notifications telling you to buy particular books; it's also opt out. I'm semi-certain other built-in apps like YouTube and the Play Store do the same. However, once you turn all that junk off, the Pixel experience is pretty good.

Why would you even enable notifications on these apps?

I'm on GrapheneOS, so they are not enabled by default, but I think on Google certified Android you can also switch them off. Also, besides that, if apps implement notifications nicely, they are nicer on Android, because you can turn on/off notifications per category/channel. Of course, some apps just put everything together.