Julia Roberts didn't return for Ocean's 13 as Tess, and here's why she was left out of the trilogy capper. Director Steven Soderbergh rebooted Ocean's 11 in 2001 with a star-studded ensemble cast. The heist movie franchise was led by George Clooney's Danny Ocean, Brad Pitt's Rusty Ryan, and Matt Damon's Linus Caldwell. The trio led a group of recurring male cast members like Bernie Mac, Casey Affleck, Scott Caan, Eddie Jemison, Elliott Gould, Carl Reiner, and Andy Garcia. However, although Julia Roberts had the biggest female role in the Ocean's movies, she elected not to return for the final original installment.
After working with Soderbergh on Erin Brockovich, Roberts joined Ocean's 11 to play Tess Ocean. She originally entered the franchise as the ex-wife of Danny and was dating casino owner Terry Benedict, who owned the three casinos the Eleven planned to rob. Danny managed to win back Tess by the end of Ocean's 11 and they were happily remarried by the time Ocean's 12 began. She didn't have as big of a role in the sequel at the start, although the movie did allow Tess to pose as the real-life Julia Roberts once she became part of Ocean's 12's heist and ending. Despite this, however, Julia Roberts didn't return for Ocean's 13.
Tess' absence from the final entry in the Ocean's trilogy was unexpected based on her involvement in the previous two films. Ocean's 13 explained why Tess didn't appear by having Danny explain that the latest heist isn't her fight. The same explanation was given for Catherine Zeta-Jones not returning, but the real reason she and Julia Roberts were left out was the size of their roles. Soderbergh originally planned on bringing Julia Roberts back for Ocean's 13, but she would only do it if it meant a sizable role. After Tess was a supporting character in the previous films, Roberts wanted to play a more active role in the story. Since Ocean's 13 director Steven Soderbergh wasn't able to accommodate this request, she didn't return.
Even though there could've been a version of Ocean's 13 with Julia Roberts in it, her exit from the franchise was amicable. She understandably wanted a bigger role in the series for the third film. Although Soderbergh wanted to keep Tess around, he wasn't willing to do so in the capacity that Roberts wanted. It was a disappointing outcome to the situation, as it meant Ocean's 13 was without its biggest female character. Since this also meant Catherine Zeta-Jones not returning, the trilogy ended with only one woman playing a substantial role, Ellen Barkin as Abigail Sponder.
Julia Roberts' Oceans' 13 absence likely won't be rectified at any point in the future. The chances of Ocean's 14 happening appear to be incredibly slim, so Tess and Danny's lives won't continue in that fashion. It seems the best chance at Roberts returning to the Ocean's franchise may have already passed. Missing out on Ocean's 13 was one thing, but she also could've been part of the crew in Ocean's 8 theoretically and work alongside Danny's sister played by Sandra Bullock. Of course, the latter would've also surely meant using Julia Roberts in a starring role, which might not have worked.