Why do skeptics cite the 'No True Scotsman' fallacy?

Why do skeptics cite the 'No True Scotsman' fallacy on every situation in which the genuineness of someone is?
Scientific Committee to Evaluate PseudoSkeptic Criticism of the Paranormal
https://www.debunkingskeptics.com/forum/
https://www.debunkingskeptics.com/forum/viewtopic.php?f=4&t=2724