The main reason a lot of idol actors suck is because they don’t actually care about acting and therefore put no effort into improving. You have idols like Baekhyun who care about singing so he puts in practice to be a good singer, and his acting is subpar because it’s just something SM shoves him into. Then you have idols like DO who actually enjoy and care about acting, so he trains for it and tries to grow as an actor. It’s just natural that you work harder at things you’re passionate about, subsequently improving at that thing. Honestly I don’t even blame the idols, it’s their companies that make them act when they obviously don’t care about it. (Also I love EXO, I’m just using Baeksoo as an example).