Ah, so famous actors aren't allowed to be offered roles unless it's a role comparable to Shakespearean?
Perhaps he's a fan, and wanted any role just to be part of Doctor Who (Star Trek Movies have several of these cameos, where actors just wanted to be part of it, and weren't worried about the role, IE: CHristian Slater and Winona Rider played Spocks mom in the new movie for about 30 seconds, hardly a deep role).
Perhaps he did it for a Grandchild/neice/nephew.
Maybe he had 10 minutes available in between movie roles and thought it would be fun.....
So what exactly is
a ''gimmicky cameo'' then? Considering the examples you gave above, aren't they all actors playing a role, no matter how small or trivial it is?