Your application uses a wildcard domain and that prevents you from using our Automated Certificate Management (ACM) feature. You would like us to support it and wonder why it's not possible.
Currently, ACM doesn't support wildcard domains as mentioned in the known limitations section of our Dev Center article. Supporting wildcard domains is something we'd like to do. Up until March 13, 2018, this was an upstream limitation from Let's Encrypt. They've since released wildcard support. We've not yet been able to implement support for this feature, but hope to at some point down the road.