I'm reluctant to criticize scouts for the decisions they make about allocating their time.
Actually, I'm kind of jealous that scouts have the luxury to make a quick decision to spend their time more wisely than hanging around to watch a player they know they aren't going to recommend.
I don't know how many times I've conducted job interviews and known in the first few minutes the applicant wasn't a good match but went ahead and gave him or her the full opportunity to overcome my early impressions. Being fair was the right thing to do, but it wasn't the most efficient use of my time.
From the accounts I've read, good scouts often have contingency games they are prepared to watch if the player they want to see doesn't play. I seriously doubt the scouts in these stories left the ballpark, went back to their hotels, and drank beer in front of the TV.
They went somewhere else and did something else they thought was a better use of their time.
Scouts are paid to form opinions about people. If they form one in the pre-game, they can say, "My work here is done," and go do something else.