Alexa (Amazon Echo) is not on the Works With SmartThings compatible / supported list (not even with the “labs” footnote), so you should have been fully aware of this at the time of purchase.
EDIT: SmartThings prominently claims compatibility in their blog, so, … on my .
Considering the effort SmartThings needs to focus on platform stability, I think it is perfectly understandable, reasonable, and very good business strategy to de-prioritize officially unsupported features and integrations … don’t you think?
In this case, I don’t know what role Amazon plays in developing and maintaining this integration. SmartThings has published a sufficient procedure for 3rd party services (like SmartTiles, any many more) to handle the cross-boarder sharding / domain URL requirements. If the integration code is Amazon’s responsibility, then Amazon Echo / Alexa customers should request Amazon implement the new specifications. Otherwise … it will go somewhere low on the SmartThings todo list.