Look, this is a foolish arguement. The only reason why the DK, Wario, and Yoshi games are covered is because they are DIRECT links to the Marioverse. Everyone knows this and understands this.
Think of Diddy Kong Racing as a Super Smash bros type game... in that there is no real story, it's just a game with crazy characters. If we go by all of YOUR logics, then Banjo/Kazooie characters/gamestuff would be listed, along with Conker characters/gamestuff, and StarFox characters/gamestuff. Why StarFox? Because it goes DK > Diddy > Diddy Kong Racing > Tricky > StarFox Adventures. Where will it end?
Think of Diddy Kong Racing as a Super Smash bros type game... in that there is no real story, it's just a game with crazy characters. If we go by all of YOUR logics, then Banjo/Kazooie characters/gamestuff would be listed, along with Conker characters/gamestuff, and StarFox characters/gamestuff. Why StarFox? Because it goes DK > Diddy > Diddy Kong Racing > Tricky > StarFox Adventures. Where will it end?