Your argument assumes workflows never change. If that were true, we would still be using whatever workflows our forebears used for every task. Since that is clearly untrue, workflows must be able to change.

However, given that business are formed to turn a profit, the standard workflow will remain unchanged until it is profitable to do otherwise.

If a markup-generating DSL was simple enough for designers to pick up quickly, it would make good business sense to push them through the transition.