The Fiend was the greatest charactar WWE's had in years. Why did Vince ruin Bray Wyatt again?

Because Stone Cold said so

Because that's what Vince McMahon does.

By your standards then WWE has been ruining The Careers of Professional Wrestlers for 7 Decades.  Was Shawn Michael's Career ruined by losing? What about Bret Hart, Triple H, Stone Cold Steve Austin, The Rock, John Cena, Edge. Randy Orton. Every Professional Wrestler loses matches, get a grip.

One loss does.not ruin a push. Every wrestler loses matches. Often a loss here and there enhances the push.

Because Goldberg gets winded 90 seconds into a match, so all his matches have to be squashes.

Because he’s not Seth Rollins or Roman Reigns. Vince has an idea of what his wrestlers should look like:  tall muscular guys like Lesnar, Rollins, Reigns. The Fiend doesn’t have that book.