I was looking at the test bowling averages for Indian bowlers:

Jasprit Bumrah: 19.42
Mohammed Siraj: 30.87
Prasidh Krishna: 26.00
Mohammed Shami: 27.71
Shardul Thakur: 28.38
Ravindra Jadeja: 24.10
Ravichandran Ashwin: 24.00
Washington Sundar: 25.20

Out of these bowlers, Siraj is the only one with a >30 average. I am not sure how he is able to find an automatic spot in the playing XI every time. Perhaps close relations with Kohli and Rohit helps.