What kind of the language should be officially used in this small island Taiwan has always been one of the most sensitive issues.  In subways and on buses, even within some public elevators, people may have been sick and tired about those obnoxious announcements made in Mandarin, Fujianese, Hakka, and English, one after another.  It is absolutely in no need of such a medley to torture people of Taiwan, whom I believe would understand the simple announcements in Mandarin without difficulties, but no politicians dare change this weird situation and touch such a hot potato.

Why not?  I think partly because no one wants to be accused of "language discrimination" in Taiwan.  You know, regardless that Mandarin, Fujianese, or Hakka are all written in the same Chinese characters, their pronounciations quite differ from one another.  But when the government stipulates any one as "national language", the others will inevitably become vernaculars, which would engender sense of inequality.  In retrospect, Nationalist China should not enshrine Mandarin as sole "national language" in the first place, though the government could promote it with no effort spared. 

CCP in China Mainland took humbler but smarter move instead.  Like Chiang in Taiwan, CCP wanted to promote Mandarin for better communication among so mass a population and so large a country, but she told the people that Mandarin is just a "commonly spoken language", not a "national" one.  It works. 

Attached below please see a reportage about the history on the unification and the evolution of Chinese language, and how has Mandarin taken precedence over other dialects at last.                         

https://www.toutiao.com/a6802499168532169230/