This is a bit like the "If you're not doing anything, you have nothing to hide" argument. You're thinking this is an all or nothing position, and it's very much not. It depends on one's threat model, but there's two sides to the coin worth considering.

First, that your entire life is open to anyone with money. Individuals so motivated can spend a couple grand and buy your advertising data and stalk you. Everything you think, every little whim, every random question, is used to build a profile on you that benefits someone else financially. All you get is free email and a mediocre browser from a billion-dollar company that derives an average of $1,600 from you a year if you're in the US ? You can pay for those services for a tenth of that. So you're 90% profit to Google.

On the flip side, by giving up so much high-value data, that profile becomes active in real time. Even if you use ad blockers and don't see the ads (which as a Chrome user, you no longer can do). You are an active target by companies. Not just you, everyone around you. Friends, family, coworkers. For some big ticket items, advertisers will target anyone connected to your profile. So your parents, your kids, your neighbors, might start to get ads about a cruise. Not for them, but for you, since it looks like you might be a good mark for a cruise. These companies manipulate people around you to be the ads, so that when you bring up "we're thinking about doing a cruise" at some point, everyone around you jumps in with the same "oh, well I've heard that XYZ Cruise company is good."

You trust a company that much to manipulate you and everyone around you without bias? With your best interests in mind? You want to cede your agency as a human to real-time auctions?

Personally, this is fundamentally abhorrent to me. And I understand that other people are fine with this. However, I'd rather leave a small and bland trail of a few occasional and useless crumbs, and then leave "redacted" as a middle finger because that deprives Google and Meta of using me as a revenue source. The nice part is that even partially masking your footprint and traffic, it's enough to break the real-time value of you as an individual. So not only does every little bit help, every little bit has effects to protect you and your family.

i2p is a separate network entirely, and part of that is routing your traffic to someone else's connection. So your exit node is someone else's laptop or server. And you're letting other people doing who knows what else use your connection as an exit node. Which, for me, is an absolute deal breaker. I don't trust other people online to let them use my connection.