I would say it's so you can be sure of getting first first time every time. Let's face it once we're past 2nd it's often hard to know what gear we are in, so kicking down to first means we know where it is.
It would still be easy to get 1st wouldnt it as it would just be all the way to the top or bottom
Let's say you're hooning it - very tight corner, down to first. And either double tap, or shift twice. Suddenly, you're freewheeling round the corner. Not good. Similarly, if you're on the motorway, and reach for "7th". and you find yourself in neutral? Again, no good.
And the reason to put it between 1st and 2nd is that you almost pull away in first, and nearly always stop in either 2nd or 1st. It's a convenient place for it to be.