Easy. Second degree is easier to prove.
"This isn't a court of justice, boy
This is a court of law"
-- Billy Bragg
If you are talking about the Oland case, JLM, I believe it is because it was not deemed a premeditated murder but a crime of passion. In the first case it would be 1rst degree, in the second, 2nd degree.
According to the CBC news channel this morning it was deemed to be for financial gain.
It may well have been, JLM trouble is that without proof that Oland had been planning to murder his Dad for awhile, it is still 2nd degree murder. From what I have heard about the trial it was never proved that the act was anything more than an argument that escalated and ended in murder.