This isn’t really specific to ACME; most CAs are happy to sell domain-validated certificates only for subdomains. It sounds like this is a quirk of DigiCert mos

This isn’t really specific to ACME; most CAs are happy to sell domain-validated certificates only for subdomains. It sounds like this is a quirk of DigiCert mostly only selling org/extended-validation certificates, or them trying to make future sales easier. ACME-supporting CAs and other CAs are all held to the same compliance standards in the end, so nothing prevents the other from doing what you want.