Apparently putting down the stones in Poland is met with resistance. If poles want to commemorate killed poles with these stones they will have to take the initiative.
There are stones like this in Poland commemorating Jews, e.g. former German city of Breslau, nowadays Wrocław. I believe the resistance came from the fact that Poles were not organizers of those killings/deportations and it was expected to be misunderstood by people unfamiliar with history (e.g. stone commemorating murdered Jews in a city that was formerly German but nowadays Polish, or Jews murdered in Poland by Germans).
Important to mention: there were killings (not supported by the state) of Jews and systemic antisemitism (clearly supported by the state) in Poland conducted and organized by Polish people before and during the war (this was, though, not supported by the state at that time), but incomparable in scale.
If you care about this, the "article" is wikipedia, and in the time you wrote this posts you could have added it already.
edit: I was quick to comment, the article is protected. So unless you already have an active Wikipedia account, you'd have to request an edit on the talk page.
It's hard to tell if this is some anti-Polish resentiments of one or many of the authors, or just extremely low level of historical knowledge, but something tells me it's the first.
In this case the stones mark the places where the victims lived.
I assume most Polish victims did not live in the territory of present day Germany.
From personal experience I recall some with "eastern" names in a town that used to have a notable polish minority but I couldn't say for sure.
Btw Can you recommend places to visit to learn more about their stories and history (besides the former sites of the concentration camps)?
Think about where we would be if we hadn't gone down this path. We can all help move things forward if we meet each other with an open mind, and steer clear of the resentment and national chauvinism of the past.