Because It is acting as a hurdle for other trains. Slow train on a route always is a "headache" like situation speedy route. Recently MTJ-KOTA-MMCT have been upgraded for 130kmph and all trains are bound to run with this speed.
Trains like Janta and Dehradun Express with almost on every 3rd station can't resist on this upgraded route. So:
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1. DDN BDTS got diverted via Chittorgarh Ratlam
2. Janta Express got cancelled.
Will not be surprised if other slow trains divert too.