I can think of a few reasons.
It sort of makes sense to have Jews in one section. The cemetery might make sure there are rocks on the ground (often along the road) so Jewish families can leave a stone when they visit the grave.
I didn’t know cemeteries break up different Christian sects. Do Catholics have different traditions than Jehovah’s Witnesses that it might be easier for the century to group them together in terms of maintenance?
Maybe some people live in a very segregated way and it feels normal to them to visit a loved ones grave like they are still in their community. I don’t mean segregated in terms of bigotry, like they keep others out, but sometimes groups tend to cluster to be near their place of worship. Plus, then when you are at the cemetery you can easily visit more than one friend or relative because they are more likely to be nearby.