Saeathak Malhar hides the baby from evil eyes of Deshmukh's
If maayi knows her kid is alive she will want baby but she won't go to sarthak back
So Anu knowing truth is also to be avoided
Hence sarthak despite Malhar needing him stays away
Malhar won't leave aurangabad due to kallu pillu yaadein
Makes sense
Rane men were never uber rich
Uppar se kala ka halath after maayi might not have been good
Wether he still practices or not is question and malhar is a sub inspector
Only house they have officially is ahaliya niwaas
Malhar had a govt quarters and sarthak intailly was in a rneted house
So for baby especially after pillus death the kid being their only happiness Malhar would stake the wada makes sense
He loves swara so much so that bachi also would be his behen and he would be over protective after pillu incident
Anu was old for a healthy pregnancy and child without mother uske koi surgery vagera kuch aaya hoga
And malhar told kallu karz li thi isilye and sudden pose
I feel that sarmal doesn't want Deshmukh's to know about the baby's existence