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.
IGS Energy was created in 1989.
Deepwell Energy was created in 1975.
TECO Energy was created in 1899.
Genel Energy was created in 2011.
Pengrowth Energy was created in 1988.
Spectra Energy was created in 2006.
Opus Energy was created in 2002.
Energy Centre was created in 1984.
Amigo Energy was created in 2003.
Noble Energy was created in 1932.
Cenovus Energy was created in 2009.