Why?

You tell me. It's not my confusion.

From what I infer, people who think deontologically already seem to reason "The most effective decision to make as evaluated by UDT is Cooperate in this situation in which CDT picks Defect. This feels all moral to me. UDT must be on my side. I claim UDT is deontological because we agree regarding this particular issue." This leads to people saying "Using UDT/TDT reasoning..." in places where UDT doesn't reason in any such way.

UDT is "deontological" if and only if that deontological system consists of or is equivalent to the rule "It is an ethical duty to behave like a consequentialist implementing UDT". ie. It just isn't.