As far as I have ever known with Metahumans, The only time it ‘Automatically Generates Cards’ is when you GENERATE a MetaHuman. The cards are avaialble to use when you switch to them. Some Hair come with the WARNING that LODS exist only for LOD 0&1. Those same Grooms NEVER come with CARDS. Whatever cards are availabe (OR NOT) are then set at that time. THE PROOF IS THE FACT THAT YOU YOURSELF HAVE CARDS FOR SOME but NOT OTHERS.
------> Are you referrring to the experimental Card Generation that was introduced in 4.26? Easy fix if you are importing Grooms or Alembic: Install 4.26,
import your Grooms, make cards for them then Migrate the Groom and Cards to your 5.1 or 5.2 project
YES I know you can’t get a Groom to go from 5.2 to 4.26 to ‘Card It’… BUT Maybe you can!: (I did some research for you, I never like to take No for an answer 
(5254) Ornatrix UE: Procedural groom export in UE5 - YouTube