Unified or not, does not matter with dialectal
classification.
You might as well say, since Thai language and Lao
language are 1 family, why not unify Thailand and Laos?
Or Czech language, Slovak language, near to each other. Go
unify Czech & Slovakia again?
Or Swedish language, Norwegian language, Danish language, near
to each other. Go unify Sweden, Norway, Denmark?
Or Pakistani language, Hindi language, near to each other. Go
unify Pakistan & India?
Or American language, British language, Australian language,
Canadian language, near to each other. Go unify USA, Britian,
Australia, Canada?
Siao ting tong lar.
Like that Singapore can unify with Britain.