The proposed KCVL-MYS train passes through KJM, BNC and SBC, which is saturated because, there are 7 more trains that run between SBC and BYPL, and take a turn towards hosur and dharmapuri. Trains like KCG-KJM can be discounted because they join the mainline only after these 7 trains divert towards Hosur. So that's why SWR is not allowing the train via this route. If SR changes the route via BYPL-BAND-YPR, SWR might reconsider, but that would defeat the purpose of running a SF train. And moreover, I don't think there's time slot available in SBC to accommodate any more trains during morning hours, that's why SWR is starting all interstate trains from BAND/KJM/BNC.