In 2375 Grand Nagus Zek retired after introducing major reforms to Ferengi society and named Rom, not Quark, as his successor.
Under the influence of Ishka, Quark's mother, Grand Nagus Zek introduced reforms during the 2370s, such as rights for Ferengi women and taxes to pay for social programs. In 2375 he decided to retire with Ishka.
Quark expected to succeed him and was horrified by the reforms. Zek instead chose Rom, Quark's brother, who would continue his changes. Rom left Deep Space Nine with Leeta to lead the Ferengi Alliance.