Remembrance and memorials alone don't stop atrocities from happening again. There's a difference between reminded of the past, and actively engaging with the past in the present moment.
It's important to give countenance to the fact that democracy, human rights, the rule of law,... in and of itself aren't measures against populism and authoritarianism. By and large, the success of the latter is tied into resentment over key social and economic factors which determine the strength of social cohesion and a sense of equity.
If a state doesn't invest in the common interests of its citizenry, over time that will create breeding grounds for people to become resentful, distrustful, tribal, isolated,... The identity politics of populists and authoritarians by and large revolve "we against them" narratives. These are incredibly easy to understand and provide a new framework of meaning and values to disenfranchised people. Minorities become prime targets because they are visibly different and therefor easy to pick out and used as scapegoats. That's what fractures an erstwhile democratic, cohesive society.
In Germany, the NSDAP only became successful after 1932, when the effects of the Depression came into full swing in an already unstable political climate of the Weimar Republic.
You're right, though, that in a way, the remembrance of the Holocaust doesn't resolve in a clear, consistent moral framework of principles. Just think about how restitution of property and real estate is still a hotly debated topic today. The crux is that questions regarding historic responsibility and guilt and how to approach them are always framed into a backdrop of present day economical and political concerns and interests. And that's just collective behavior that can be changed with an easy silver bullet fix.
> Unfortunately I think part of the popularity of these stone today is that they are no longer provocative.
I highly doubt that. On an individual level, humans are very much capable of feeling empathy and compassion. For instance, the Auschwitz-Birkenau memorial received a record 2.3 million visitors in 2019. The unspeakable atrocities that happened there still resonate to this very day. If not for countless children and grand-children still deal with a lost connection to their own shared past through the loss of their family in the camps; and the stories that are still begin shared publicly of that great sorrow.
The thing that should worry us is people either not even noticing the stones and their significance in the first place, or forgetting their significance the minute they've passed and falling back into biased thinking regarding present day state of the world.