Background: En Vogue is an American R&B/Pop vocal group whose original lineup consisted of singers Terry Ellis, Dawn Robinson, Cindy Herron, and Maxine Jones. Formed in Oakland, California in 1988, En Vogue reached number two on the US Hot 100 with the single "Hold On", which was taken from their 1990 debut album Born To Sing. The group's 1992 follow-up album Funky Divas reached the top 10 in both the US and UK, and included their second US number two hit "My Lovin' (You're Never Gonna Get It)", plus the US top 10 hits "
Context: In 1995, En Vogue was amongst numerous African-American female vocalists featured on the song "Freedom" for the soundtrack to Mario Van Peebles' drama film Panther (1995). Also in 1995, while band members Cindy Herron and Maxine Jones went on maternity leave, Ellis recorded and released a solo album entitled Southern Gal, which spun off the top ten R&B single "Where Ever You Are." The same year, the band also made a cameo appearance in Joel Schumachers superhero film Batman Forever. In 1996, En Vogue recorded "Don't Let Go (Love)" for the soundtrack to the motion picture Set It Off, directed by F. Gary Gray. Released as the soundtrack's lead single in the fall 1996, it became the group's biggest hit yet, selling over 1.8 million copies worldwide and becoming certified platinum by the RIAA. In response to the large commercial success of "Don't Let Go (Love)," the group steadfastly went to work on their third studio album. As the album was nearing completion, Robinson chose to leave the group in April 1997 after difficult contractual negotiations reached a stalemate. Despite Robinson's abrupt departure, Ellis, Herron, and Jones resolved to continue on as a trio.  Robinson's abrupt departure from En Vogue forced the remaining trio to re-record several of her original lead vocals on their forthcoming album EV3, which was released in June 1997. A breakaway from previous projects, it marked En Vogue's first project to include a diverse roster of collaborators including credits from Babyface, David Foster, Diane Warren, Andrea Martin, and Ivan Matias along with regular contributors Foster & McElroy. Upon its release, EV3 received mixed reviews from critics, many of whom praised the band's vocal performances but were critical with overall production of the album. In the US, it reached the top ten in Germany, Switzerland, and the United Kingdom and debuted at number eight on both Billboard's Top R&B/Hip-Hop Albums chart and the Billboard 200 with sales of 76,500 units, the band's highest first-week numbers. Two further singles released from the album, "Whatever" and "Too Gone, Too Long", entered the top twenty and top forty the Billboard Hot 100, respectively.  In 1998, En Vogue recorded the song "No Fool No More" for the soundtrack to Gregory Nava's romantic drama film Why Do Fools Fall In Love (1998). A top forty entry on the New Zealand Singles Chart, it was later included on the band's first compilation album Best of En Vogue, released in June 1999. A moderate success, the album reached the top forty in Austria and the United Kingdom.
Question: Why did Robinson Leave?

Answer:
Robinson chose to leave the group in April 1997 after difficult contractual negotiations reached a stalemate.