Production Car challenge = gr86 cup

Why does everyone drive a gr86, and we have barely 5-6 mx5's and 0-4 m2's. if everyone wants to drive gr86 this bad why not just go drive the gr86 cup. does it depend on the free tracks, this week gr86 is on a paid track. Is this always the case or it changes depending on track. And also, no clio's but I was expecting that.

(This is my first week racing these series so I don't have anything to compare)