I can think of at least 3 reasons for not using CMS/PKCS #7: 1. CMS is using ASN.1 as others have mentioned. That alone is a deal-breaker and a major reason CMS

I can think of at least 3 reasons for not using CMS/PKCS #7: 1. CMS is using ASN.1 as others have mentioned. That alone is a deal-breaker and a major reason CMS implementation are hard, uncommon, and ever-so-slightly incompatible. 2. CMS requires certificates, which are harder to generate, verify and deal with than simple public keys. 3. CMS allows you to use any combination of ciphers, including weak one. Experience with TLS told us that this flexibility is NOT good feature when it comes to crypto standards. Besides that, all the reasons the rationale raised against PGP also reamin true for CMS: https://saltpack.org/pgp-message-format-problems https://saltpack.org/pgp-message-format-problems