Why did Brian Jones become less influential in the Rolling Stones?

Although Brian Jones was the original driving force and most gifted instrumentalist of the Rolling Stones, his influence within the band waned significantly as the group evolved.1

Several factors contributed to his marginalization:

• Shift in Creative Control: The band’s transition from performing blues covers to writing original material placed Mick Jagger and Keith Richards in firm creative control. Because Jones lacked a talent for songwriting, he became increasingly sidelined as the Jagger-Richards partnership became the group's primary engine.1
• Personal Struggles: Jones struggled with drug use, which eventually rendered him a "depressive, drug-sodden liability" in the eyes of his bandmates.1
• Interpersonal Difficulties: Beyond his substance issues, Jones had a reputation for being self-centered and difficult to work with.2

While his "textural wizardry" remained a highlight on the 1966 album Aftermath, his overall creativity and influence declined thereafter. These factors ultimately led to his dismissal from the band in June 1969, shortly before his death.12