I tested with the current CNET installers, and that Spigot folder you refer to is indeed removed by the current version of Malwarebytes Anti-Malware for Mac. That folder is something I've known about for quite a long time; the earliest versions of AdwareMedic removed it. Even the AppleScript precursor to AdwareMedic, my Adware Removal Tool, removed it.
I can't comment on why it didn't get removed for you. Perhaps that item got inadvertently unchecked in the detection window before you did the removal, or perhaps you had a permissions problem that prevented it from being removed. I don't know. Whatever the case, though, your experience is not normal, and something unusual happened.
I can't comment on why it didn't get removed for you. Perhaps that item got inadvertently unchecked in the detection window before you did the removal, or perhaps you had a permissions problem that prevented it from being removed. I don't know. Whatever the case, though, your experience is not normal, and something unusual happened.