Short answers, pulled from the story.
Konami Computer Entertainment Tokyo established Team Silent in 1999 and dissolved the group in April 2005. The team operated within the larger Konami structure for six years before management chose to end its existence deliberately.
Keiichiro Toyama directed the very first Silent Hill game which launched in 1999. He departed Japan Studio shortly after the release to create the Siren series.
Team Silent released their debut title in 1999 followed by a second entry the next year. Silent Hill 3 arrived in 2003 and Silent Hill 4: The Room concluded the original run in 2004.
Management chose to dissolve the group deliberately to have Western developers produce future entries instead of Japanese staff. This move signaled a strategic pivot away from domestic talent toward international studios like Vatra Games.
Akira Yamaoka left Konami in 2009 to join Grasshopper Manufacture where he continued composing music for various projects. In 2017 he stated that reunification with former colleagues was unlikely due to changes in technology and industry mindset.