Why people from Malwa region mostly report their mother tongue as Hindi rather than Malwi ?

I see in most of the districts in Ujjain and Ibdore Divisions - 25% to 50% people only report Malwi-Nimari as their mother tongue. In the most advanced Indore district number drops to just 15%. More strangely Malwi just disappears in Bhopal division, which becomes like 100% Hindi region ! Wasn't this region historically the part of Malwa ? **Any idea about the reasons behind this?** Also comparing Malwi to the sister languages Rajasthani and Gujarati. In Rajasthan districts we see 80-90% people reporting their mother tongue as Rajasthani or Marwari etc. And Gujarati is a full fledged language itself.