That’s because stop motion software has features that are dedicated to the creation, capturing and fine-tuning of stop motion. Ideally, (and this is what they do professionally) you’d use the stop motion software to grab frames, preview, re-shoot, and tweak your animation while you’re in the process of doing it. Once you’re finished, you take your footage and do the editing in a separate video editing suite. Essentially, stop motion software is a production tool and video editing is post-production. In commercial work like movies and TV they use a third and separate audio editing suite to do the sound mixing. It’s more than a little unfair and unrealistic to ask one program to have have the full features of a stop motion, video AND audio editing programs.