I think most people (or at least those who choose 7, which I definitely used to do) associate 'randomness' with 'uniqueness', and since lots people would consid

I think most people (or at least those who choose 7, which I definitely used to do) associate 'randomness' with 'uniqueness', and since lots people would consider 7 to be the most 'unique' number between 1 and 10 (When considering things such as divisors and how often they are used), they pick that number as it feels the most 'random'.