The LORD

Why has WELS decided to remove Yahweh's name and replace it with Lord?

I do not know what kind of “decision” of WELS you are referencing. The Jews, going back to at least the third century B.C., substituted “Adonai” (“LORD”) for Yahweh. Respect for God led the Jews not to pronounce “Yahweh” or “Yahveh.” Because of that, we do not know with certainty what vowels were tied to the four consonants of that name. Many Bible translations have continued that practice of substituting LORD for Yahweh/Yahveh.