I would imagine that 99% of people wouldn’t be happy with a service that is 99% spam.
And besides, for something to be spam you need to actually see it. In the case of notifications if you deny the permission on a site you don't see the notifications. That's the perfect spam filter. Imagine a world where people could only send you email if you explicitly said you accepted it from them. Or if robocallers could only call you if you agreed first. Spam would be over. There would be no spam. That sounds fantastic.