It is much more critical to sell fast than to sell a lot. Take the example you someone building a new house. When you build it, you pay for two houses: your current, and the next. Near the end of the construction, every single week is critical for your budget. Because you have a high loan, and zero benefits out of the new house. This was development of the wii. This is investment.

Now, you start living in your house. You need to refund the bank. The faster you give the money back, the fewer interest you will pay. And at the end of the day, your house will be cheaper if you pay it in 7 years than if you pay it in 20 years. Same for the wii: nintendo is now paying for the development. Once they managed to refund the development, they start to earn money, and they can get even more benefits of that money (develop new products, buy buildings, ...). And you enter a virtue circle.

If you sell very little at the beginning, you will have to sustain the high costs of daily business + refund investment for a longer time. Which means that you will not have capacity to invest, that your product will have to remain expensive. And ultimately, a new product will be released and you will be out. That's why taking 5 years to be a blockbuster is usually not an option, and that's why you see so many efforts to sell products exactly when they are released (movies, games, houses, ...)