Birch hardwood floors have always been a popular choice due to the fact that they are cheaper than oak, but are still a hard-wearing hardwood floor with a variety of natural colors. It’s worth looking at some birch flooring photos online so you know what I mean. As you can see, it is very different from oak flooring, however both floors are the most popular solid woods being sold today.
I think it’s compensation. Just price over product. Oak is strong and durable, but more expensive. Birch is a cheap floor, which is not as strong (or beautiful) as oak. People choose it because of the price. Maple would be a better choice for a lightweight floor than birch as it is more stable and more wear resistant, but doesn’t sell as much volume. And that means it’s simply because of the price.
Of course, now that engineered and multilayer flooring is becoming more popular, oak flooring has become even cheaper. But engineered birch flooring would also become cheap hardwood flooring if it only made it to hardwood flooring in good volume. But as it is, it is still a niche and therefore a very expensive product. And if that’s not weird enough, due to the lower volumes, this less-high-grade engineered wood is considerably less expensive than its oak engineered flooring rival.
A good idea of how a lower quality product can become more expensive due to volume. I would say buy the oak any day. And if you really like tough but light flooring, buy some maple.