That's where all the good record labels and record producers were. All good Canadian musicians/actors/directors go to the US. They largely leave Canada behind without much mention of Canada during their careers besides Drake and to a lesser extent Neil Young being the exception.

Leonard's first album had amazing production by american producer John Simon (who also worked with The Band, Simon & Garfunkel, Janis Joplin), probably the best in Cohen's entire career, so he chose well deciding to work out of Columbia's studio in NYC...

https://en.wikipedia.org/wiki/Songs_of_Leonard_Cohen