Realistically, it’s because oda likely didn’t plan on kid even being in wano.
Oda probably planned on Big Mom and Kaido to get separate arcs; however, realizing he didn’t want to write that he combined it. Seeing how odas initial plan was Doffy being Kaidos powerful ally it makes sense if Luffy and Law vs Kaido and Doffy was the initial plan. Then when oda decided to make wano the end of both wanos he just slapdashed Kid in it with no build up to make big moms defeat logical for the arc. And now that he’s kinda pointless going forward oda just killed him off
Oda probably planned on Big Mom and Kaido to get separate arcs; however, realizing he didn’t want to write that he combined it. Seeing how odas initial plan was Doffy being Kaidos powerful ally it makes sense if Luffy and Law vs Kaido and Doffy was the initial plan. Then when oda decided to make wano the end of both wanos he just slapdashed Kid in it with no build up to make big moms defeat logical for the arc. And now that he’s kinda pointless going forward oda just killed him off