[interestednovice]

Yes, the rationale is twofold, really:

1) EE gets a much higher Net Promotor Score (NPS) which is marketing speak for brand resonance. So customers have a more favourable view of the EE brand. The CEO of BT Consumer is Marc Allera who is an ex-EE person too, so he probably grasps better than most that EE is better regarded by customers.

2) It’s a more modern brand, as you say, which is more closely associated with mobile and broadband-only (mobile broadband, etc) products. This works well for marketing things such as hybrid broadband which you can then sell to people as “not your grandad’s broadband”! This helps to sell the products as “premium”.