This is not a consistent trend at all. As per the final placements statistics of the 2017–2019 batch, the major portion of IIM Ahmedabad went for consulting than that of IIM Bangalore.
This is why IIMB consists mainly of students with good work experience.
Many of these students have come after working at firms that are industry leaders in their domain. Consulting firms prefer candidates with work experience, especially the ones who’ve worked in companies as industry leaders. Thus they may be willing to roll out more offers at IIM Bangalore.
It may be true that IIM B received more consulting offers in certain years but it may not be correct to accept this as a general trend across years.