Question

why indian constitutions came into effect on 26 january 1950

Answer 1

The Constitution of India came into force on 26 January 1950. ... The Constitution was adopted by the Indian ConstituentAssembly on 26 November 1949, and came into effect on 26 January 1950 with a democratic government system, completing the country's transition towards becoming an independent republic.

Answer 2

Because every constitution need some time to be prepared and also our nation India got freedom on 15 August 1947.
The time interval of 2 years 11 months and 18 days is normal to make a constitution