Pages is a strange beast. It's one of the only tools in Tableau that just doesn't quite work the same way as everything else and it often has some strange results. In this case, I *believe* that pages requires it to show all of the possible dimension values in your data set in order to work properly. In an ideal world, Pages would just act like a sort of point-in-time filter. When the value changes, it updates the filter and that filter just works like any other filter. But, unfortunately, that's just not how it works.
I know that's not a great answer...
That said, here's an approach for "racing bar charts" that may work for you (though it is a bit complex): https://greatified.com/2019/03/20/how-to-build-an-animated-bar-chart-race-in-tableau-software/