This.
First, you start with the talent pool, which is very low on minorities and females.
Then you cut off the 95% bottom part, as these companies get more applicants than the average tech company, and can be somewhat more picky. You have even fewer (not because women or minorities can't be good, but certain demographics statistically do better at showing off their strengths in the shark pool).
Now of whats left, these companies have a biais to hire ultra monitivated/no work life balance/eat and dream computer science people. That cuts off anyone whom's life doesn't revolve around the field.
And then the coup de grace, they favor younger applicants, and women and minorities usually have kids younger (the gender age gap stereotype of women usually dating older guys doesn't help here...it means usually the woman will be significantly younger when they have kids). So a young man is more likely to not have kid than a woman of the same age, and thus will have more time to dedicate to the career.
All that together means you end up with white males, asians and indians. Its just the correlation between these groups and the criteria the hyper-competitive companies use to hire that cause this.