My guess is that an online platform cannot sell polarized because there would only be two workout variations: Z2* and some form of 4x4, 4x8, or 4x16min intervals. People would question why they are paying $20/month for what they can easily program on their smart trainer or do outside. They would even question the value of a power meter doing the Seiler polarized plan because it’s not needed for those workouts.
Edit - Yes Z2 in a 5/6 zone model. Z1 in a 3 zone model.