Because he's nothing of the sort. He's an isolationist (more or less), which is a stance designed to look like pacifism but in fact is very different, and has all kinds of negative side effects, one of which is that it ultimately leads to war, or tolerance of things worse than war (and which is always fake populist stance anyway). See also:

https://en.wikipedia.org/wiki/America_First_(policy)

Seriously - remember when he said he would "make Mexico pay" for the wall he wanted to build? Exactly how do you think he would "make" Mexico do that? Is that a "pacifist" stance?

Or is he just making stuff up, to blow smoke in your face and push your buttons?

If Trump's brand of pacifism means negotiating with Russian terrorism, then it's not peace but the cuckolding of a nation and millions of people that lived through a period in time when the Soviets were actually a superpower. Peace when Russia is down and begging for violence would be an imbecile's decision.

Are we supposed to sincerely acquiesce to the demands of a humiliated nation that turned a "special military operation" into a blood feud with hundreds of thousands of casualties?

   In the interview, which took place on Sept. 11, 2002, Stern asked Trump directly if he was for invading Iraq.

   "Yeah, I guess so," Trump responded. "I wish the first time it was done correctly."

That would be quite helpful indeed.