Why wasn't Gollum turned into a wraith?

[Landroval]

Sauron, especially in his earlier days as Annatar, was a very RATIONAL being. He wouldn't do something against his own interests just because of his 'evilness".

Well, he did refuse the summons of the valar after the war of wrath, because of his evil side. And one way to read Myths Transformed is that evil is a subcategory of stupidity

The wielder of one of the Nine in the Third Age would have become a wraith, but not Sauron's servant.

Hm, the way I interpret the various mentioning of "wraith" in FotR, for example, is that it represents complete obedience to Sauron.