The Spice Girls are an English pop girl group formed in 1994. The group originally consisted of Melanie Brown ("Scary Spice"), Melanie Chisholm ("Sporty Spice"), Emma Bunton ("Baby Spice"), Geri Halliwell ("Ginger Spice"), and Victoria Beckham, nee Adams ("Posh Spice"). They were signed to Virgin Records and released their debut single "Wannabe" in 1996, which hit number one in 37 countries and established them as a global phenomenon. Their debut album Spice sold more than 31 million copies worldwide, becoming the best-selling album by a female group in history.

While on tour in the United-States, the group continued to record new material and released a new song, "Goodbye", before Christmas in 1998. The song was seen as a tribute to Geri Halliwell, and when it topped the UK Singles Chart it became their third consecutive Christmas number-one - equalling the record previously set by the Beatles. Later in 1998, Bunton and Chisholm appeared at the 1998 MTV Europe Music Awards without their other band members, and the group won two awards: "Best Pop Act" and "Best Group" for a second time. In late 1998, Brown and Adams announced they were both pregnant; Brown was married to dancer Jimmy Gulzer and became known as Mel G for a brief period. She gave birth to daughter Phoenix Chi in February 1999. One month later, Adams gave birth to son Brooklyn, whose father was then Manchester United footballer David Beckham. Later that year, she married Beckham in a highly publicised wedding in Ireland.  The Spice Girls returned to the studio in August 1999, after an eight-month recording break to start work on their third and last studio album. The album's sound was initially more pop-influenced, similar to their first two albums, and included production from Eliot Kennedy. The album's sound took a mature direction when American producers like Rodney Jerkins, Jimmy Jam and Terry Lewis came on to collaborate with the group. In December 1999 they performed live for a UK-only tour, Christmas in Spiceworld, in London and Manchester, also showcasing new songs from the third album. During 1999, the group recorded the character Amneris' song "My Strongest Suit" in Elton John and Tim Rice's Aida, a concept album which would later go on to fuel the musical version of Verdi's Aida. The band performed again at the 2000 Brit Awards, where they received a Lifetime Achievement Award. Despite being at the event, Halliwell did not join her former bandmates on stage. In November 2000, the group released Forever. Sporting a new edgier R&B sound, the album received a lukewarm response from critics.  In the US, the album peaked at number thirty-nine on the Billboard 200 albums chart. In the UK, the album was released the same week as Westlife's Coast to Coast album and the chart battle was widely reported by the media, where Westlife won the battle reaching number one in the UK, leaving the Spice Girls at number two. The lead single from Forever, the double A-side "Holler"/"Let Love Lead the Way", became the group's ninth number one single in the UK. However the song failed to break onto the Billboard Hot 100 singles chart stateside, instead peaking at number seven on the Bubbling Under Hot 100 Singles. "Holler" did peak at number thirty-one on the Hot Dance Music/Club Play chart in 2000. The only major performance of the lead single came at the MTV Europe Music Awards on 16 November 2000. In total, Forever achieved only a fraction of the success of its two best-selling predecessors, selling five million copies. In December 2000, the group unofficially announced that they were beginning an indefinite hiatus and would be concentrating on their solo careers in regards to their foreseeable future, although they pointed out that the group was not splitting.

Using a quote from the above article, answer the following question: why did they take the hiatus?
the group unofficially announced that they were beginning an indefinite hiatus and would be concentrating on their solo careers in regards to their foreseeable future,