Methane is NASTY stuff. Unlike the gas in your stove - to which an acrid odor is added - you can’t generally smell methane easily, and it cleanly REPLACES the oxygen in your lung alveoli, so you don’t realize you are suffocating, until you black out and it is far too late.
That’s why you need a canary.
Kinda like CO2 which fools your lungs into just not operating.