Answer by taking a quote from the following article:

Napalm Death are a British extreme metal band formed in Meriden, West Midlands, England, in 1981. While none of its original members remain in the group since December 1986, the lineup of vocalist Mark "Barney" Greenway, bassist Shane Embury, guitarist Mitch Harris and drummer Danny Herrera has remained consistent of the band's career since 1992's Utopia Banished, although, from 1989 to 2004, Napalm Death were a five-piece band after they added Jesse Pintado as the replacement of one-time guitarist Bill Steer; following Pintado's departure, the band reverted to a four-piece rather than replace him. Napalm Death are credited as pioneers of the grindcore genre by incorporating elements of crust punk and death metal, using a noise-filled sound that uses heavily distorted, down-tuned guitars, grinding overdrive bass, high speed tempo, blast beats, and vocals which consist of incomprehensible growls, or high-pitched shrieks, extremely short songs, fast tempos, and sociopolitical lyrics. The band's debut album Scum, released in 1987 by Earache Records, proved substantially influential throughout the global metal community.

Their EP Greed Killing was released through Earache in December 1995, followed by the album Diatribes in January 1996. There was greater animosity between the band during this time, with a rift between Greenway and the remainder of the band, especially over the band's stylistic transition and the interference of background presences in the band, exemplifying the former when he stated that the band were "letting go of what made the band special". Greenway was hence expelled from the band later in 1996, and went to record with fellow grindcore act Extreme Noise Terror (ENT) on their release Damage 381. Greenway has stated that following his expulsion he was "devastated" and did not want to commit to ENT in fear of a repetition of the events that took place within Napalm Death.  ENT's vocalist Phil Vane replaced Greenway in Napalm Death. Alas, Shane Embury stated that Vane "couldn't pull off what was required. It was a hard day when I had to pull Phil aside and tell him it just wasn't working. We had been too much into doing our own thing to acknowledge all of the parts that made the Napalm machine tick. I quickly made the call and asked Barney if he would rejoin--time away certainly gave all of us the chance for reflection, regrets and hopes for the future. He was surprised by the material, as it was heavy and some of the songs were fast--I don't know what he really expected us to do!". Following Vane's departure, Greenway returned and the band released the album Inside the Torn Apart on June 3 1997. An EP and music video were released for the album's track "Breed to Breathe" on November 17 1997.  The album Words from the Exit Wound followed this, being released on October 26 1998. The album was their last to be produced by Colin Richardson, who Embury believes hindered the album's creation, ultimately affecting the album's success. Embury has stated that bands such as Nasum influenced the album, and in Embury's view, this album represented a turning point in the band's sound, stating "it was also a turning point in us moving towards rediscovering our roots." Embury also mentioned that following the album's release, the band found it hard to tour due to restricted budgets from their record label, but fortunately for the band, Cradle of Filth and Nick Barker were able to alleviate this problem.

Why did Greenway leave the band in the first place?
rift between Greenway and the remainder of the band, especially over the band's stylistic transition