I actually don't really believe in the Church's disciplinary infallibility. Despite being the common opinion of theologians, it remains an opinion. I find it interesting that when the Church defined infallibility, She only bothered to do so regarding Her solemn magisterium. Why not just tell us clearly that Her universal laws and rites are also dogmatically impeccable? She didn't bother and it wouldn't have been that hard. Makes me wonder. Even about the Universal, Ordinary Magisterium.
Even if it hasn't been defined, that's objectively heretical and will be condemned as such when this all blows over. So, according to you, the Church can fail in her mission of saving souls by, oh, promulgating a Mass that offends God and brings harm to souls, or establish a cult for "saints" who are likely in Hell and at the very least were enemies of the Faith. It's terrifying to see how many of you are losing the faith. That's to say nothing about how idiotic it is to assert that because Vatican I had not defined it ... yet ... that it isn't true.
Dogmatically impeccable? That's not a thing.
As for why not define it ... well, Vatican I was interrupted by various wars the Masons started to interrupt it. So they may have gone on to define it. But even if they chose not to, that could be fur any number of reasons. Even with what they did define, there were many inopportunists who didn't think it should be defined, even while believing it to be true.
God permitted them not to define it to be a test of faith today ... one that you are failing.