Why do things the Borg don't need to do to achieve the goal they're attempting to achieve?
The Borg sent 1 cube because if they lost the cube it was a pittance and they'd learn something about whomever destroyed it, and if they didn't lose the cube then then they had an extra cube lying around.
The Borg didn't invent ranged weapons because they didn't need them. They simply dont' care if they throw away the lives of 100 drones. And in all likelihood they won't because they'll have adapted to whatever their enemy is using to attack them in any case.
Sometimes I think people simply fail to grasp exactly how vast the Borg Collective is and, given their mentality, how little even thousands of lives mean to them. Hell, there's a VOY episode where the Queen is blowing up her own ships almost casually.