I will try to answer it systematically with the last point being the most important one.
1)Dermatology is a clinical branch,hence if someone has got good rank and is not willing to go for med/surg etc and also want some “Clinical Doctor Type Feel”,then dermatology is best among the lot(Radio and anaesthesia provide all other things,except the clinical doctor type feel-accoeding to larger population).
2)Its not an emergency branch.So,the people who want cool life will definitely take it.
3)Since its not an emergency branch,so generally girls take it, as it also gives ample opportunity for family time also.
4)Now the most important part-the seats of MD Dermatology in India are very less.Yes you read it right ,they are almost one third/one fourth of medicine /surgery and about half/third of pediatrics/ortho.So,it gives a false impression from counselling list that it fills up early,where as in reality if you compare side by side it goes to lower rank then Medicine/Pediatrics.In simpler terms,since seats are less,hence even if lesser percentage of people taking it ,still it fills early whereas due to more seats in medicine/pedia even if relatively more number of people taking it,the list goes far behind.