Lol it's not a rocket science to tell why. The main reason is LYD needs a younger partner not necessarily Choi. Why I said Choi is, LYD plays with him in national tournament and iirc they won this or last year. I am not saying Choi is the best partner of LYD but with a younger partner like Choi, he may atleast win the first round in intl tournaments.better for lyd specifically? based on what? age, age difference, specific skill set, complimentary skill set, future career path as a pair, club affiliation, nat'l team standing...?
Play hard. Train harder.