I'm only speaking for myself. Here are a few reasons:

I know I should tech him, but don't have the balls.
I have the balls, but am not sure if I should tech him.
I made a bad call and want to give him some slack.
A tech is a big call and I don't want my assignor/the AD to not assign me games in the future.
I want the coach's vote for the state tournament (varies by state).
I was focused on something else and didn't realize he was yelling at me.
2 points and the ball is a big deal, especially at the end of a close game.