I've got Sport1 and also noticed they don't list the Juve game on their website, but they often refresh their schedule a few days before the actual weekend. Usually they list all the EPL games ( because they show every single one of them ) but don't list the Serie A or Primera Division games till thursday or even friday. I pretty sure ( and hope.. ) they will show the Lazio-Juve game, because it's a 'big game'.
I see what you mean though.. they even show Ligue 1 games sometimes, instead of an evening Serie A game, which is absolutely ridiculous.