Why do we get braces on the lower teeth despite being properly aligned?

I got my braces on upper teeths 1 month ago, then after when i had an visit to my dentist he suggested you should get braces on your lower one's also for the support, so i need to know even if the lower teeths are properly aligned, why he said to have braces in lower teeths? and that too after 1 month..They are so irritating as compare to upper one's..

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