Low sperm count and puzzled

I really don’t get it. If we only need one sperm to get pregnant, then why does having low sperm count matter? I have been getting a bit frustrated for the past few months of TTC and it makes me question why out of my husband’s 1.3mil sperm count (which is considered very low by the way) not even one can make it to the egg.

Funny isn’t it. 😔