ADC Mid Question

Been watching some proplay games during Jan-March of this year, spring split mainly LCK and LPL and had a question. I noticed that whenever one team picked like Corki mid, or any other adc mid, why did the other team lock in Quinn against those adcs in mid lane? I saw a game OMG vs WC and WC picked Corki mid and then OMG last picked Quinn against corki? Any reason why they didn't just go an AP mid instead?