Fuller House was never to shy away from making fun of the Olsen Twins and their absence as Michelle in the show, but they cut a particular joke in season 1 supposedly delivered by John Stamos' Uncle Jesse, why? Throughout its five-season run, fans of Full House held out hope that somehow Mary-Kate and/or Ashley Olsen would do a surprise cameo in the spin-off even just for one time. But even as the series ended with the joint wedding of DJ and Stephanie, alongside Kimmy, the youngest Tanner sister was nowhere to be found.
After Netflix officially greenlit Fuller House, there had been a lot of conversations regarding whether or not the Olsen twins will appear. Conflicting reports came out about their potential involvement making things more complicated. Rumor had it that Ashley wasn't interested at all, while Mary-Kate was a little bit more open to the idea but ultimately decided to not do it. Having moved on from acting and are now focused on being fashion designers, the Olsen Twins simply didn't want to revisit their past as actresses.
Instead of beating around the bush, Fuller House quickly explained why Michelle wasn't in San Francisco with her family in the premiere. Mining inspiration from Ashley and Mary-Kate's real job, the youngest Tanner sister was apparently also a fashion mogul in New York. But the show pushed it further by breaking the fourth wall and looked at the camera; it's not meant to be a diss, but it felt like it. In fact, they were planning on taking it further (as per People) with Uncle Jesse complaining about their absence, shouting "one episode," referring to only needing a brief cameo from the sisters and they couldn't even oblige. Then, Stamos' character supposedly got a sudden call from "the twins' lawyer." Clearly from the get-go, Fuller House was not one to miss any opportunity to poke fun at the situation, but this specific joke may have been deemed too much, especially considering the status of Stamos' relationship with the Olsens around that time.
Aside from starring in Fuller House, Stamos also served as an executive producer; long before that, however, he had been attempting to revive Full House, so understandably, having Netflix greenlight the sequel was a big thing. When he personally confirmed the news in 2015, the Olsens revealed shortly after that they weren't aware of the project until it was publicized. Stamos refuted this, implying that the twins knew that it had been in the works. Belatedly when it was officially announced that Mary-Kate and Ashley were not partaking, he also elaborated that every one of the cast was approached; while he understood that the Michelle actresses have moved on from their acting days, they "only need one," meaning just one of the sisters would be enough. Despite Stamos insisting from then on that he has had a great relationship with her former co-stars, it sounded as if there was still some animosity between them. Having Uncle Jesse break the fourth wall and make a very pointed jab could've made things worse.
It's also worth noting that around this time, Fuller House producers were still trying to make a Michelle cameo possible. After the first season, there were still rumblings about the possibility of them changing their minds and making a cameo. For the show, that means still consistently referring to them to keep Michelle somehow involved. Unfortunately, that surprise appearance never happened, and as it became increasingly clear that they won't be involved in any way, the spin-off also gradually decreased mentioning the character. In any case, this wasn't the first time that Stamos was at odds with Mary-Kate and Ashley as he also almost tried to fire the Olsen twins from Full House.