Because numbers 1, 2, 3, 4 and 5 have as much chance as winning as 32, 33, 34, 35 and 36, which have as much chance as numbers 1, 14, 25, 37 and 49.
There is no logic in choosing your numbers as each as an equal chance as coming up.
But when was the last time a draw was made when no numbers above 31 came out?