Because Taylor Swift is like a highly advanced computer program that learns from its mistakes.
She let Nicki Minaj bait her into response. Taylor Swift recalibrated her settings, and now has a firewall against trolls. And that's what Miley Cyrus was doing with her comments with "Bad Blood." She was trying to bait Taylor Swift into a response (and to gain buzz for the VMAs). And if Taylor Swift did respond, Miley Cyrus would just fall back on the "I was just talking about how women are portrayed, not Taylor Swift" card like Nicki Minaj did (even though they're both just being petty and attacking Taylor Swift because she's the #1 pop star in the world and did it without being naked or twerking for men).
Taylor Swift is too advanced for that. She's a higher life form. She's not responding to any one else on the matter. Not Katy Perry's tweet that made her look dumb as a goldfish, and not Miley Cyrus passive aggressive comments in a magazine.
Sending them love, though.
...Vin