I think bookmakers are afraid that India may lose momentum during the 2nd innings. They have seen how poorly they played in the 2nd innings and therefore, they aren't confident enough to give high odds to the Indian team. However, this may change quickly if India bat the first two sessions tomorrow and increase their lead to over 400-450.
India has lost 4 wickets for 236 runs. but infact, we can say that they have lost 5 wickets because Rishabh Pant was retired hurt. He was batting well on 31 and it was big blow for the Indian team. This is crucial moment for the Indian team. If they lose some more wickets quickly, they would be on backfoot again.
India must have to score 400 runs in first innings to stay in the game. Although India lost 4 wickets on day one but Rishabh Pant is retired hurt and if he is not available for batting in first innings then not much batting is left behind. Shoaib Bashir is not playing this test and England relying mostly on seamers in this test. So far seamers have done good job for England by picking wickets and not allowed India to score too many runs. Tomorrow is crucial day for India, they have to make sure they score too many runs on day 2.