Comment by ilyt

DNS challenge is required for wildcards on LE at the very least.

But the reason for HTTP is pretty simple - it's extremely easy to implement. You only need to tell your ops to redir a subdomain to your app and you're done, you don't need DNS with API that have narrow enough permission to allow that one team in whole company to generate ACME stuff; most providers ACLs on DNS end at "this client have acesss to that domain via API".