Because she couldn't create as much hype around her releases as the other girls did, it's as simple as that. But in the long run she always has nice sales and she has a lot of hype around herself, and as a result she has longevity and nice tour numbers. That being said, y'all are something else acting like Beyoncé is some kind of flop or something just because she didn't join a very limited club of girls that opened above 1 Million
Reality is, Beyoncé is one of the most successful acts around regardless of her 1M+ openings or lack thereof!