What could be the reason that they put mayonnaise along with sauce with momos in my city Bangalore but they don't in Siliguri?

In our city Bangalore, I have noticed that literally every momo vendors put mayonnaise along with sauce to dip the momos while eating but in my hometown Siliguri and Falakata, they don't put mayonnaise with momos. They only put sauce there. The momos in Siliguri are too yummy. I usually prefer eating momos without any sauce or mayonnaise tho. What do you think could be the reason behind putting mayonnaise with momos in our city?