Sarcastically, no one should.

Unsarcastically, a lot of people believe user data belongs to users, and that they should have a say in how it's used. Here, I think the point is that Niantic decided they could use the data this way and weren't transparent about it until it was already done. I'm sure I would be in the minority, but I would never have played - or never have done certain things like the research tasks - had I known I was training an AI model.

I'm sure the Po:Go EULA that no one reads has blanket grants saying "you agree that we can do whatever we want," so I can't complain too hard, but still disappointed I spent any time in that game.

Maybe they trust Pokemon as a IP? Usually Nintendo keeps your data safe.

Because not everyone is a seasoned IT professional.

I'm not a fan of the way you moved the goal posts here. You argued that Niantic would obviously use user data to fund game operations. Then we see that they don't actually need to do that, and that the game could fund itself. Then you argue that well, we shouldn't assume that they wouldn't try to monetize user data, shame on us. I agree that those who know how tech companies operate should be extremely pessimistic as to how users are treated, but I don't think that pessimism has permeated the public consciousness to quite the level you think it has. Moreover, I don't think it's a failing on the part of the user to assume that a company would do something in their best interest. It's a failing of the company to treat users as commodities whose only value is to be sold.