If consumers don't understand technology, perhaps the technologists don't understand the consumerism
In short, it takes a lot of money, time, expertise, and many sales connections to put a product in a store. Eneloop can either:
*Hire a sales division and spend a few years setting up sales
*Hire packaging designers and spend a few years producing brand presence
*Pay out buckets of cash to slip their cells onto Energizer/Duracell's shelves (See below)
*Hire advertising space and try to sell a product to the masses on technical merit
*Set up distribution network and get long-term contracts
*Compete with their partners who presently do all this work for them
Lots of big-box stores have requirements for their products. For example, Lowe's only buys nuts and bolts that come in bags of 100-200 so they can fill their bolt bucket drawers. They are sometimes paid a lot of money by Duracell or Energizer (Depends on the exact store) to pretty much solely stock that brand of batteries. And finally, what store manager would waste 50% more space on "yet another battery display?"
Sanyo makes good money producing batteries for rebranding companies like Energizer. They wouldn't make as much selling direct to consumers in stores.