We live in a time when there's less gender inequality than there used to be (but only 'less'). At the time that it was mooted to put the L first, the world was even more loaded in favour of men, so it made even more sense back then to try to adjust the loading wherever possible - hence, for a change, putting women first. Nowadays, we're more familiar with that happening a lot, but back then it was kind of radical.
That's how I've heard and read the history behind LGBT, anyway.