There are many users including myself were this would be a disadvantage.
I hold two investment accounts, one taxed, one untaxed. These accounts hold many of the same securities. Being able to set different Subtype’s allows me to differentiate the security as a taxed or non-taxed holdings. In reports these are splits into two sections which would not possible if I could only set one subtype per security.
Other users may well use the flexibility that setting different types allows.