Speaking at Mar-a-Lago, Trump said that he has “agreed” to three debates in September
Former President Donald Trump spent nearly an hour at his Palm Beach, Florida, social club on Thursday ranting to a room full of reporters as he tries to grab the spotlight from a resurgent Democratic ticket fronted by Vice President Kamala Harris and Minnesota Governor Tim Walz.
Because lying means the liar knows they are lying. Stating a falsehood means you don't have to have the intent of lying.
This comes down to libel. Journalists would like not to get sued because they think someone is lying instead of just claiming things they believe in, misguided as it is.
that he actually knows that was a falsehood when he said it?
To call something a lie, you basically have to be inside the person's head. You have to know not only the action, but the intent. That's, really, really hard to prove in a way that satisfies the (legitimate and necessary) requirements of journalistic ethics.
When they sue you for libel, they will have to prove that you knew you were lying and still went ahead with it, in order to damage or disparage the other party.
This goes the same for Trump: can you prove he knows he's lying?
Edit: in other, better words:
The legal definition of lying is that someone spread false information with knowledge that the information was false.
In general, a journalist cannot establish whether a person did or did not have prior knowledge, so we don't use the term. It keeps us from getting sued.
The journalist can say he lied, then state factual data -- but then real life happens and someone points out this action is subjective, biased and is attacking some person. Maybe the journalist also needs cred power for people to believe his stance.
So to address objectivity in journalism, reporters just say what happened. No backtracking. No side references. Maaaaybe also pushed you their job to make sense of what it is.
There's also a factor about sponsorship and money but that's just money talk.