Because if energy conservation is NOT valid, then this would be equivalent to the laws of the Universe changing over time. The details of this relationship are complicated (some advanced math); if you know a lot of math, and are interested in this topic, do some reading on Noether's Theorem. If you don't know the advanced mathematics, you can still get a general overview.
JSW Energy was created in 1994.
Agri-Energy Roundtable was created in 1980.
EDF Energy was created in 2002 when the UK branch of the French energy firm EDF acquired London Energy and Seeboard.
Sapphire Energy was created in 2007.
Sudden Burst of Energy was created in 1996.
JSW Energy was created in 1994.
Freeplay Energy was created in 1994.
ExAlta Energy was created in 1975.
Stream Energy was created in 2004.
Energy - event - was created in 1992.
RRI Energy was created in 2002.
Shipley Energy was created in 1929.
Shining Energy was created in 2004.
Pioneer Energy was created in 1956.
Bloom Energy was created in 2002.
CS Energy was created in 1997.
Ambit Energy was created in 2006.