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.
Now I can see why the bookmakers weren't considering India as favourite. Their batting line-up has collapsed in the first innings. England is playing a lot better now. The openers played in Bazball method and made a great partnership. England might end their first innings with a decent lead. The odds is completely in favour of England now. I guess I'm going to lose my bet which I placed on India on the first day of the match.