I assume that this habit originated in ancient times when not everyone could have a drink of hot tea. At the same time, hot water is available to anyone. But in our time, tea is available everywhere, I would have made a choice in favor of tea.
I also thought that at that ancient time people notice if drink boiled water, then people get sick less(as you say boiling water will kill a lot of harmful bacteria and other micro-organisms.).
PS
Because they love their babit
Babit?
PPS I'm sorry that I'm so meticulous...
Thank you! Edited the error.
Whilst boiling water does kill bacteria, drinking it doesn't necessarily help to cure illnesses. More of a prevention.
༼✿ @sweetsssj
Yes, its only prevention