Why does postgresql flexible server SKUs not conform to standard names?

Why does the does sku_name for azurerm_postgresql_flexible_server not conform to standard Azure RM sku names? According to the documentation the provider requires you to prefix the sku_name with the tier. See below…

  • sku_name - (Optional) The SKU Name for the PostgreSQL Flexible Server. The name of the SKU, follows the tier + name pattern (e.g. B_Standard_B1ms, GP_Standard_D2s_v3, MO_Standard_E4s_v3).

I am very curious as to why this decision was made as it causes quite a bit of confusion for those who use arm/bicep templates. How am I supposed to find the tier prefix when even the azure cli doesn’t even mention a tier? SEE: az postgres flexible-server list-skus