When Bray Wyatt launched his 'Fiend' gimmick in 2019, he wore a tortured expression during 'Firefly Fun House' segments and explained that "he" was a manifestation of his pain. When Triple H changed into 'The Game' in 1999, he described a nagging need to be taken seriously. Hell, even Michael Cole only stopped being a heel nuisance on commentary in 2012 because Jerry Lawler's very-real heart attack had shaken him to his core.
Nobody on this list could/can boast a reason anywhere near as solid as those.
Every single one of them changed gimmicks suddenly and without any concrete explanation from WWE on television. There's a fair chance Vince McMahon looked at each switch during creative meetings, shrugged his shoulders and said something to the effect of, 'Who cares why they've changed? Just change it!' to his writers.
Perhaps he had a point, because some changes were for the better. Most, however, weren't - that's why they're here to begin with. They're head-scratching reminders of times when McMahon and company decided to keep fans in the dark and move on without proper closure...