Default Account Id in reports

Two comments here.  First, while in Rules Engine it is true that Account ID is typically required, that is actually not the case in Reporting.  To pick just one example, it would be quite normal to build a report of open CTAs by CSM.  No Account fields used at all.   Second, while we do pick default Account lookups in some situations, it is actually trickier than it sounds because there can be more than one account lookup on an object.  This is why in Rules Engine there is an option to switch which Account ID is used.