[tidepod12]

>only to get turned down with an explanation that was known at the beginning. How many interviews does it take to come to that realization?

The explanation likely wasn't known at the beginning. The thing that changed was the other candidate, and the company almost certainly had no way of knowing if this other candidate was going to fill the role up until the moment they did, at which time (I'm assuming) is when the company cancelled OP's presentation. The company likely had full intention to hire OP until that point.

>It seems like this should be true, and I hope it is, but I have worked for companies that seem to interview just for the sake of feeling or appearing to move forward in filling a position. Maybe the recruiter or hiring manager is incentivized in that way? Some action, even if it's in the wrong direction, is perceived as better than no action at all.

That's opposite my experience as a hiring manager. If we're "iffy" on a candidate, we'll likely give another interview to see if the first interview was a fluke. But if it's already known off the bat that the candidate won't be hired, we certainly don't waste time interviewing them anyway. Interviewing someone that's already a "no" means wasting multiple peoples' entire day in interviews, meetings, debriefs for no progress. That's something I want to avoid as much as humanly possible, and although I'm sure it happens some places, it's definitely not incentivized at any of the companies I've worked at.