Why do people say "THANKS A LOT" instead of "THANK YOU SO MUCH"?

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Each time I hear somebody say "thanks a lot" my brain makes a flashback and it gives me a picture of the roses and daisies in my garden LOT. See a 'lot' is a piece of land, not a phrase to use instead of much.? That speaks clearly to us of the importance of what we say to others. Emily Dickinson said "A word is dead when it is said, some say, it just begins to live that day." The words we say may have long-term consequences, Our comments, our compliments, and even our harsh criticisms may stick with the hearers/readers for a long time. Do you thinks we should use the word MUCH more often? What do you think?