Why would Bitdefender make a registry key so hard to remove ?

http://www.bitdefender.com/solutions/free.html

I tried out Bitdefender when I was worried recently about malware. It did its job ok, but I saw no need to keep it installed all the time. So, I uninstalled it using Revo Uninstaller which normally does a perfect job at uninstalling everything. Some things it will not detect, so you have to use the Windows uninstall tool or just use the provided uninstall tool that comes with your chosen software.

I thought I was done with Bitdefender. Damn thing kept showing up in my Services panel and it would not let me just disable it. I used regedit to try to find and delete all traces of Bitdefender, since every trace of it was gone from my hard drive. It would not let me delete it.

Finally, I rebooted into Safe Mode, ran regedit again, and deleted the freaking registry key. GONE. The weird thing is, EVERY FREAKING BIT OF BITDEFENDER WAS OFF MY HARD DRIVE, so the registry key was useless. I don't get it. Just annoyed the piss out of me. I understand making antivirus somewhat immune to malware attempts to disable it, but this was just plain ridiculous. Next time, I'll try running regedit in Administrator mode from the system32 folder.