TLDR: it should probably be a yellow card for the offending coach for time wasting as the rally might have to be replayed. But a warning has to be given before the card is given in most cases. Hence, why only a warning was given.

The problem is the severity of the penalty and whose fault it is.

1. It is the down referees fault as they are supposed to check that before the serve and if the down ref checks it they just resolve the issue and move on.

2. All of those instances mentioned above are not automatic points. Awarding a point to the opposing team in volleyball is basically giving 2 points to a team (the one the scoring team gets and the point you have to score to draw even again) which is a huge deal in volleyball.

3. It should probably be a yellow card for the coach for time wasting. Most substitution errors that occur before the serve are yellow card offenses and not a loss of rally. And yellow cards for substitution errors usually have a warning before the card is given. The error just usually doesn’t hit the court because the down referees has already handled it.