It's political. Nothing else. They oppose the rail line wherever there is different government in centre and state and approve where there is same government in both places.
Similar Forest issue can be seen in making Marwar- Mavli rail line which will pass through forest area but it's long pending demand of people of the region to make BG which will connect not only those 2 places but also Jodhpur/ Bikaner/ Jaisalmer / Barmer to Udaipur and further to Ratlam and Indore via a shorter route.
Rail line is possible through...
more... dense forest or wildlife Sanctuary and IR has done it at other places too, like that in Achanakmar wildlife Sanctuary, connecting Anuppur to Bilaspur.