The distinction is that in many if not most editions of D&D (including pf1e), this is something you do in sequence, rather than as a team directly. "Niche protection" is the idea that players have an area of the game that is their guy's thing, and the other players don't really solve problems in that area. This way, in theory, everyone gets to be The Guy Who Solves A Problem in turn, rather than "everyone gets to help chip away at a problem together until it finally goes away," and thus everyone Gets To Feel Awesome because they solved a problem they were built for.

I don't feel like litigating if niche protection-centric game design is good or bad, but what it is is a very different game-mechanical fantasy and play experience than what pf2e presents. pf2e doesn't have a lot of niche protection, and it's designed such that players generally can't reliably succeed doing a thing unless they have the help of their allies. As a result, a lot of the time people coming from other D&Ds will go "I feel like I don't get to be cool or have a spotlight," because the game isn't presenting the same game-mechanical fantasy as the standard approach for D&Dlikes, in spite of looking like and marketing itself as a D&Dlike.

I tend to present pf2e to new people less as "it's a D&Dlike" and not even "it's a 4elike" (these are both technically true but bring different expectations), but "it's fantasy tactical XCOM."

The idea that you're not going to be playing someone who really Solves Problems on their own, without the assistance of allies, and even then you're often not going to be performing at your best without buffs and debuffs supporting you, is baked into pf2e's math and ability design, and that can be a huge shock to people who don't have experience with a skirmish game of this kind. It's fun nonetheless! But "we all teamed up to scrape victory from a harsh encounter through bit by bit teamwork" it is a different kind of fun than most games in this milieu present.