Because the real present is constantly moving. To prevent confusion several sciences use 1950 as the present, so if somebody quotes an article where something is radiocarbon dated as 80 years BP, you don't then have to look up the age of the article.
http://www.nature.com/news/laser-fusion-experiment-extracts-...
For only a hundredth of a second, and not even remotely economically viable yet. But it's a step in the right direction.