Communicating your wants and needs effectively is rewarding in itself and you actually see it with Abby (or used to, she has kind of given up). She didn't want to do something, so she signed break. When that didn't work, she went with all done, bye (when the camera was in her face) and eventually bathroom. She was going through signs that made the current activity stop. It wasn't mere coincidence either, as this happened multiple times.
Long story short, either Asshat is a dumbass who has no idea how anything related to learning works or he is pulling tit out of his oversized butt or both...
She also scrolls specifically through food-related signs (e.g., eat, pretzels, popcorn, cookie, candy, fish) when she wants a snack, or travel-related signs (e.g., go, cart, car, swing) when she wants to go somewhere. She's been communicating this whole
bleeping time, despite how limited they've allowed her vocabulary to be. He either wasn't paying attention, or was too dumb to make the connections.
(Or he was motivated to stay too dumb to make the connections, like when the comment section had to point out to him that maybe if Abbie signed "go" after walking away from him, hiding in a corner, signing "bye," and signing "all done," maybe, just MAYBE, she meant for HIM to go AWAY. Of course he wasn't going to accept that his Sweet Girl was telling him to get out of her face. He only started acknowledging it when the comments section made it hard to ignore, and even then, he started ignoring it again and pretended it was somehow a revelation when someone pointed it out again several months later.)
He's also been obsessed with the idea of her "making sentences" for a long time, as if that makes her communication so much better, but yet again he is mistaking "better" for "more like a neurotypical person" rather than "better for Abbie." I think she could communicate her personal needs and wants just fine using telegraphic language like she does now...what would make her communication more effective for her personally would be to have a larger vocabulary, and a better understanding of when/how to use it. We've seen that she has the ability to basically categorize nouns into different concepts, and adapt her limited signs to fit different situations, so I believe she's capable of using a larger vocabulary...she's just never been given a real chance.
Also...wait, I just noticed that he said despite Zaxby's being her #1 request, we've never actually seen her get it in the vlog. But I'm pretty sure we saw P take her out for Zaxby's at least once, right? It was nighttime and they were in the office and Abbie requested Zaxby's so off they went? There was also another time when they came back from Zaxby's and P talked about how she had gotten Asa a salad because it wouldn't matter if it got cold...I'm not sure if that was the same time, or a different instance. And I love how that's his big winning argument. "She might request Zaxby's all the time, but you never see her get it! Just because she requests junk food, doesn't mean we give it to her! Never mind all the many, many meals of junk food that you have seen her consume! You have never seen her specifically eat a Zaxby's, which is definitely proof that she hardly eats junk food at all! Pay no attention to the man behind the curtain!"