From what I understand and not trying to read any of the answers to this.

For the large part of the picture, it's about marketing. To market specifically to you that is based on where you've been, what you've bought before and what your interests are. So they know that you don't want to buy or subscribe into things you've no interest in at any capacity. So why not try to goad you into it by using things you're into because of the data collected that's filtered from your interests?

That's probably the only not-so worrisome thing I can think of. It's just a giant distraction and tool to get you to spend and subscribe.

A lot of people don't like to be tracked and having data collected because, we feel it isn't anyone's business in what we do. So, why should it be the business of Google, Apple, Microsoft, Discord, Reddit, Facebook, Firefox .etc to be concerned in what we do?

Aside from marketing, it'd be a lot easier for all of them to pinpoint exactly what we do to feed data to authorities for easier prosecution. Which depends on how you look at it, I just think that if you don't want to attract the attention of authorities who've been given a tip on you without you knowing, don't be a criminal.

All in all really and I'm starting to derail my own explanation, it's a big wiry issue with privacy.

To put it plainly, it's largely for marketing and we really feel it isn't the business of corporations to know what we're doing, if we're knowingly not breaking any laws. Also now that I've thought of it, harvesting so much data increases risk of security breaches that hackers can take. Which means it's going from bad hands to worse off hands because now hackers can just sell our data around in the black market and we wouldn't even know it.