I also tried Amazon Germany as Koch Media released it there once but couldn’t see it.
My general rule-of-thumb is that there's usually a German release, probably in a few different formats. I've found some really obscure films that only have a German release outside their country of origin.
At least they try and explain why a North America release might not happen:
So why is it so hard to find? Part of me wonders if DiCaprio and Wahlberg might be ashamed or wary of revisiting some of the more unseemly aspects of the film. One thing worth noting is that the film has a vivid fantasy sequence where Carroll fantasizes about shooting up his high school, and this sequence, at the time, was widely thought to have been one of the things that inspired the Columbine shootings. The misogyny and casual racism of the film might also shock some fans of the actors, especially when it comes to Mark Wahlberg, who notoriously is a convicted felon for a racially motivated attack when he was a teenager.