Why is the gram no longer a function of the atomic mass number?

According to Wikipedia,



> 
> ... the definition of the gram is not (as of 2011) mathematically tied to that of the atomic mass unit
> 
> 
> 


Why did we change that? 




Unless I misunderstand the question, the gram was never defined that way.


For historical reasons the SI unit for mass is an oddity:


1. The base unit is not the gram, but the kilogram. This is the only case where the base unit has a prefix. The gram is defined as $\frac{1}{1000}$ of a kilogram.
2. The kilogram is the only remaining SI unit that is based on a man-made object, the [International Prototype of the Kilogram](http://www.bipm.org/en/bipm/mass/prototype.html).


At its 25th meeting in 2014, the General Conference on Weights and Measures (CGPM) has (again) declared its intention to abandon this atificial standard and link 



> 
> the definitions of the kilogram, ampere, kelvin, and mole to exact numerical values of the
>  Planck constant $h$, elementary charge $e$, Boltzmann constant *k*, and Avogadro constant $N\_A$ […] 
> 
> 
> 


([Source](http://www.bipm.org/en/CGPM/db/25/1/))


One of the possible approaches for the redefinition of the kilogram would be a side-effect of the redefinition of the Avogadro constant with in the [Avogadro project](http://www.ptb.de/cms/en/presseaktuelles/journals-magazines/ptb-news/ptb-news-ausgaben/ptb-news/news05-3/avogadro-project-first-isotope-pure-silicon-single-crystal.html). 


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