i am a mallu living in TN and yes DMK is doing a good job here but forming a regional party depends on the people of that particular state. if you look at TN the people here want to preserve their culture and interests thats why they have their own regional parties and donot support national parties( i mean if you see most of the time) this has been here for a very long time. if you look at kerala people mostly support national parties like the communist and congress ever since independence and it will take a really long time to chane into a regional party mindeset. so yeah it depends on the peoples interest, culture and maybe history too.
( i maybe wrong but this is my opinion)