Why are Personal Distribution Lists not migrated?

Exchange Personal Distribution Lists (Personal DLs) allow users to create lists of recipients. We do not support migration of personal DLs for two reasons:

No API support: Microsoft’s official position is that programmatic access to Personal DLs is not supported. This means that there is no support for reading or creating Personal DLs using web-accessible APIs.
Technical limitations: Personal DLs specify members using complex binary properties. These properties specify the entry IDs of contacts, internal users, private/public distribution lists, and one-off email addresses. All entry IDs become invalid after migration to the destination system. For example, a member public DL may not be available at the time of migration while a member contact may have a different entry ID, etc.
We are currently unable to migrate Personal Distribution Lists (Contact Groups).