If carriers really wanted to get out of the phone market then they should do it. I personally do not think the cost of the phone was hidden in the plans. Carriers are making money on the phones they are selling at retail, probably double..
As far as swappa, eBay or places to buy near new used phones, I think that is going to be more difficult now.  The phones are more expensive, people like me that upgraded every year are going to hold onto their phones longer, or at least keep it for back up for the second year, the note 7 recall taught a lot of people the importance of having a back up phone. The fact that contracts are gone, someone can't get that phone for $300 and flip it for $700.  The lack of contracts will be the biggest reason your not going to see many new released phones on swappa, and I think that is the true reason behind eliminating 2 year contracts.  I think your going to see more phones a year old or older on swappa, once the warranty is over and someone is getting a new phone. Once the phone is a year old, check places out like Walmart, third party outlets, you might be able to get it brand new for same or close to same price as swappa, and its new with warranty.  
It will be an interesting ride, the Samsung S8 is getting ready to come out, betting you won't see many on swappa with the contracts gone.  You will see a few from buyers that decided they didn't like it after the 14 day deal.