Or maybe it is because there are many researchers who have actually studied the data and found that environmental factors play a large role. A summary of some of the research in this area:
I'm not disputing the role of environmental factors, I'm just questioning how the potential role of genetics has been diminished in this study without justification.
Also, from your link the only study with ability to isolate causation (the adopted korean study) found "23 percent of educational attainment is determined by environment, implying that up to 77 percent is determined by nature.".
Also, from your link the only study with ability to isolate causation (the adopted korean study) found "23 percent of educational attainment is determined by environment, implying that up to 77 percent is determined by nature.".