Yes, there are few reasons.
1. Train don't have maintenance in MAS. So no need to move to yard. BBQ yard is more busier than MAS station. Saves Yards space.
2. It is not peak hour. Platforms are available during that hour when mail stays in PF4. 2A will be occupied by Shatabdi, and 4 by Mail. Rest all platform are free for use.
Only...
more... by 6.30 7, traffic becomes heavy with TVC mail coming to PF5, GT occupying PF3, Cheran will be in PF10(Navjeevan which arrived), HWH mail in PF 9(Coromandal that arrived), ALLP in PF6.
So as such Mail doest create any issue, it will be sleeping peacefully, and by time traffic becomes heavy, its time for mail.
Mail will be parked ahead of end point, so TNP will come and push it back to end. Then around 7.30-45, P4 will takeover.