You have unknown people that can't be identified. More common than you think. They generally get buried in these locations because you don't want to lose the body in case their identity is discovered. Then you have quite a few more that they don't initially know their next of kin and it can take months to find them. These are people that pretty much have distanced themself from their family and it even friends or could be elderly and have few associates. No one claims then. In this case they need to bury them because you can't wait months to find someone. It is the respectable thing to do. And often when relatives or friends are found, they may be happy to leave them in that location. Then you have prisoners. I would be curious on the average age. If the average age is say 50, and life expectancy for a prisoner is 70, then you would expect a 5 percent attrition rate. That is not nefarious.
Point being there is not enough info in this article to determine if this is at all unusual. And your anger over finding friends and relatives might not be justified.
I personally had a brother in law died that was a heavy drug user. He stopped contacting family ten years earlier. It took agencies about a month to determine who he was related to. It is not that simple.