Icy Manipulator vs Jayemdae Tome?
Player A could use Jayemdae Tome in response.  But doing so limits their options.

If I counted correctly, Player A has 7 mana sources on the field.  That means that using Jayemdae Tome would use over half their mana.  This will severely cut down their options for what they can do in their turn.  Even if everything in their hand is cheap or useless, this is happening before Player A draws their card for the turn, so they could potentially draw something useful... and then be unable to play it.

Doing so would also shut Player A out of one or more colors, so even if they have enough mana to play the card they draw, they could easily have the wrong mana to do so.

This is especially important if Player A is using a lot of reactionary spells, such as instant speed removal and counterspells, because there's a lot of advantage to be gained by forcing your opponent to play around what you might have in your hand, and that advantage is lost if your opponent knows that you can't play any cards.

Of course, it's also possible that two players are not as strategically observant as they could be, and are just forgetting that that is an option.