If I were to makes one guess...
my guess would be one word, "LIABILITY". In other words in our current society where it isn't uncommon for folks to file obscenely ridiculous suits in an effort to profit at the expense of others, such a practise as allowing folks to fish at night would be ripe for the picking.
"Fly-fishing has many attributes, but none more pleasing than it's ability to liberate the young boy that still hides within me and to let that boy live again without embarrassment or regret, sorrow or anguish." Harry Middleton