I read that there is an effort to define a kilogram in terms that can exactly be reproduced in a lab. Why has it taken so long to get this done? It seems this would be fairly important.

Edit

Today I got around to finding the references.
You can see the international prototype of the kilogram IPK is the artifact whose mass defines at present the SI unit of mass here. You can also go here where you will see a link on the possible future revision to the SI. It sounds like this may happen in the next few years. I am not surprised that it takes years of R&D and millions of dollars to do this. Well that's peanuts compared to what was spent on LHC. I am not saying LHC was not worth the cost. It just seems we could have a modern definition of a kilogram by now if a few governments wanted to make it a priority. Does anyone here know if this effort has been given the investment that it deserves?