Neutral Evils are unswappable because their win conditions are tied to their roles.
Neutral Specials are unswappable because they're special.
Neutral Pariahs are unswappable because Town having access to Neutral Pariah roles very likely ain't a good thing (though it'd probably work fine).
Horsemen are unswappable for, and I quote "UI bugs"
Town Traitors are unswappable because the game forgets they're a Town Traitor apparently?
Egotist is unswappable because... umm... checks notes wait why is Egotist unswappable?
Egotist is just a Town role in the Egotist faction.
Egotist Amnesiac can remember Town Cursed Soul, which allows it to swap once because it can't be swapped with.


