Here is proof that it is an intentionally-bad feature:

Web pages can tell if you enabled notifications.

The last time I checked, Slack used this to break unrelated functionality until you gave it browser notification permission, and re-broke itself if you disabled permissions after enabling them. Otherwise, there is no reason to enable it or install the app. (You can deny notifications per app, at least on apple platforms).

One of the most impactful things I've done with enterprise security, and I mean moreso than buying any expensive product, was deployed a browser policy that disabled browser notifications (and deployed ublock). Service desk calls from people claiming to have been hacked because their browsers kept popping up scare ware ads dropped to nothing overnight, with a notable drop in complaints and absolutely zero complaints logged about people who wanted notifications on something. It's obscene, the desktop notification feature has generated more work for security people than active directory and it's lack of mfa support.

I was thinking the exact same thing. Nobody want notifications. It's just a way for sites to spam ads.

The fact that you have to have a seperate warning for spam messages proves that the notifications system itself is a design flaw.

They’re plenty useful when used by a service you engage with. I run Slack as a tab in my browser rather than as a standalone app and browser notifications make that usable.