This wasn’t explicitly due to his portrayal of Lenny Luthor, but rather co-showrunner Robert Rovner seeing Cryer being able to craft a villain folks hate to love.
Rovner and Jessica Queller added to EW they’ve been pleased with Cryer’s performance thus far, and thrilled that DC eventually let them bring the villain to Supergirl.
The Supergirl showrunners believed Jon Cryer was the right man for the job, and revealed he was the top choice to play the iconic villain.