The user attribute can only be set at creation time, and by default can thus not be set at all.
This view is already existing in template / plugins : we should consider inheriting the new defaut creation view

Projects can do this to workaround

<!-- Creation -->
<view name="creation" internal="true">
           <item ref="user" />
           <item ref="firstname" />
           <item ref="lastname" />
           <item ref="orgunits" />
</view>