Another issue is that ATT is way too big to care about the small marketshare that WP has. All resources and effort are spent on a million dollar player who needs a fix, while the underdog can play just a little longer...and longer....
Here is my thought on this debacle:
WP already has a relatively small market share and low numbers among AT&T customers. Then, from that take the number of WP users who have 830's. Then, out of those, consider how many know about Denim or W10M, or care about it. It's probably almost nil. AT&T probably knows that even if they have to refund or replace the devices of their customers complaining about it, it's still less cost than fixing the problem (in other words, providing full Denim and later W10M).
Another possibility is that a class action lawsuit is filed against AT&T on behalf of their 830 customers. If I were one of those customers, this would be the last thing I would want to happen. What usually happens is that the lawyers get half of the settlement, and the "victims" divide the rest, which amounts to a tiny amount each. A couple times I've had settlements come through as a credit on my credit card. Each time I can remember, the amount was less than 1 USD.