Because they weren't Slavs.
And where do the polish babies fit in? They couldn't have "worthless blood" if they were deemed to "replenish" the aryan stock.
And being blonde was for sure no sign of german blood or half of the ruling baggage would had had to be sent to the camps because they didn't had any!
I just think that the whole slavic angle of the Nazis got mightily skewed during 70 years and doubtful, still missing documents like the "Generalplan Ost" are now presented and seen as "facts".
Hitler would surely had preferred to have the Poles on his side, as he was even invited and took part in the funeral of Pilsudski whom he officially highly respected. A proud Slav to boot!
As I said, something doesn't add up here...
...Hitler repeatedly suggested a German-Polish alliance against the Soviet Union, but Piłsudski declined, instead seeking precious time to prepare for potential war with Germany or with the Soviet Union. Hitler, who admired Piłsudski's leadership and his successful coup, also kept hoping to meet personally with Piłsudski, but again was rebuffed.
Anti-Slav racism looks different I would say....
In 1939 when the Germans took Kraków Hitler ordered the Wehrmacht to set at Piłsudski's grave a honor guard.