A 2.1 developer profile system doesn't have a default-config, so when this is upgraded to 3.1, it is expected to not have a default-config either. If the user wants to use clustering features in 3.1 based on an upgraded 2.1 developer domain, they have several options:
1. Use the 2.1 feature to upgrade the domain to the enterprise profile before upgrading to 3.1.
2. Create a default-config in 3.1 using asadmin copy-config command.
Creating a default-config automatically as part of an upgrade would involve an assumption that the user actually wants that created as part of the upgrade.