Warum Christian Allaire während seiner Buchtour ausschließlich indigene Designer trug  

(Alternatively, for a more formal tone:  
Warum Christian Allaire auf seiner Buchtour ausschließlich Kleidung indigener Designer trug)  

*Note*:  
– The phrasing can be adjusted slightly depending on context .  
– “Indigenous” is translated as “indigene”  or “Designer indigener Herkunft” if specifying heritage is preferred.  
– German often uses the Präteritum  for written narratives, but Perfekt  would also be correct in spoken/casual contexts.