We have that "idea" because BioWare has described their tie-ins as being part of an overarching universe.
Corporations lie to make money.
You may have found it tedious, but I enjoyed reading about Admiral Anderson. And I wouldn't have bothered reading about a Shepard who's a completely different gender from mine.
To each his own I suppose. Wouldn't bother me to read someone elses interpretation of Shepard, so long as the games themselves continued to accomodate mine.