Existing customers Forced to Leave Xfinity mobile

I currently am looking to get new phones for myself and family but all of the deals offered are only for new customers only. Not for existing customers. I want to stay with Xfinity but I feel I’m being forced out because I can get such great deals on new phones from other carriers. Buy one get one free, trade in old phone, get a new phone. These deals can save me more than $3000 if I make the switch. Why would I stay? Why doesn’t Xfinity ever have anything for existing customers?