Because they’ve stated that on many, many occasions. The only time they /might/ have any idea is on metadata retrieval, which is highly anonymized. Their relationship to you is highly a “Don’t ask, Don’t tell” one.

You could, and others have, spent time sniffing Network traffic to see what data goes out and when to confirm for yourself.

If they did know, they would place themselves in the spot of policing what is on your media server (and how it got there), rather than being the platform and leaving it up to each individual to collect, rip, and store their mass collection of blu rays.