That is certainly not true in all cases. It's possible that there's a second choice candidate, and the hiring manager wants to extend an offer to them as soon as the other candidate declines.

Probably more common is an experience I was in- we found a good candidate, he wanted to finish other interviews before making a decision and I gave him a few weeks to decide, then later I regretted giving him so much time. It meant I had to either pause the candidate search for a few weeks or potentially waste my time and candidates' time interviewing people when there may not be an opening.