Your animal was kept in poor conditions before you got it, in addition to having the parasites you mentioned. What happens in those cases is that the poor conditions weaken the animal's overall system so that the parasite load balloons out of control, and the animal winds up succumbing. Treatment will sometimes help but in most cases it will just cause excess stress to the animal's already compromised system.
From the other threads, you did a great job of providing better conditions than Abraxas had been living in before. Since you had him/her for such a short time, the battle most likely had been over before the animal even arrived on your doorstep.
If you are still willing to give monitors another shot, the best thing I can recommend is to support captive breeders and start with a species that has more reasonable caging requirements. What you will find out is that the situation you just had with Abraxas is constantly being repeated, as wild caught animals are imported and farmed. The only way to make a difference is to not support the cycle of diminished wild populations, and, ultimately, dead/sick animals.
Captive bred Ackies are becoming a lot more popular, they are all the fun of larger monitors in a two foot package. Though the initial price tag is higher, in the long run they are less costly to support. Planning ahead will give you time to hang around message boards and see other people's enclosures, which you can then plan to build.
I'm sorry for your loss, it sounds like you made every attempt to do the right thing.