Tyranny of the majority.
True, however smaller manufacturers like Zowie and Mionix manage to sell quality ambidextrous mice. Unfortunately, none of them come with the 3366 sensor yet, and they have their own minor annoyances and issues.
If all a company cares about is profits and not fulfilling a customer need, then by all means they should neglect the 10% of the market that is crying out for one, just one, decent ambidextrous or lefty mouse. Those who do it capture a significant portion of that smaller lefty market vs a mere fraction of the much more competitive right-handed mouse market.
Logitech got close with the G900, but it's built for palm grip, not claw or fingertip (a smaller version would be perfect, again Zowie takes this approach). Banging two buttons on a G303 would be the ideal, lightweight, no-fuss gaming mouse. I use the G303 myself, but would really like those extra two buttons.
It's not like they need to do any design revision other than slotting a couple of extra $2 switches in there. They had the chance to do it on the G200, but it's another opportunity lost for those who need the freedom of choice the most. There are literally hundreds if not thousands of gaming mice that we lefties simply can't use, whereas righties are nothing short of spoiled for choice.