Well, I would say for a couple of reasons:
1) Cost. At this time since 2ohm components are scarce, the cost to manufacture them is more. Then, consider that most people still believe that '4ohm sounds better than 2 ohm' and it's a tough press to convince people to buy a high end 2ohm component set. Manufacturers don't usually like to fight uphill battles.
2) Performance. Many people have asked about, and been stressed about, their speaker (usually sub) being too high an impedance. An example would be someone with a DVC 4ohm and an amp that does not do 2ohm mono so they have to go 8ohm mono. I always encourage them to try it and have never been told that it was unreasonably quiet.
I have even demonstrated two woofers, side by side running off one amp switched back and forth, one 4 ohm and the other 8 ohm, and you have to listen carefully in a listening room to really be able to tell the difference in output. The theoretical difference is only 3db which is just barely noticable by many people. Consider that 8ohm speakers are often a db or two more sensitive than a 4ohm counterpart and that margin dissappears.
Having said this - a 2ohm component set will likely have marginal if any perceptible output advantage from an identical 4ohm set yet it does still run the amp twice as hard, has to dissipate twice the power from those tiny 3/4 and 1" voicecoils, etc.
Overall the negatives outweigh the perceived advantages most often.

And for the gallery - I'm not saying impedence does not matter, just that people might place too much emphasis on it.