Why did DLG replace Asquith as PM in Dec 1916?

Why did DLG replace Asquith as PM in Dec 1916?

DLG's background

Asquith was PM continuously from 1908 to Dec 1916 but he headed a coalition government from May 1915. DLG  had been his most prominent minister of Chancellor of the Exchequer from 1908 to 1915. 

Asquith-A crisis

Then, there was a crisis over munitiions shortages on the Western Front in May 1915, and DLG became the new minister of munitions. His energetic action soon helped to increase production and made his reputation as…