While the Commander format supports a sizable number of viable strategies, staple archetypes such as Control are just as powerful in Commander as they are in formats like Modern or Legacy
This means that each instance of damage, whether it be combat, activated ability, or spell, will either cost an additional mana or two life
You cast this card, make your opponent lose 1 life, cast another ally, make them lose 2 life, and so on
Blue can draw the most, sure, but it also has many, many redundant effects and cheap options on the curve that can do other things
This is something you can do in green ramp but it requires some work in the build and may not be supported well in the cube you are playing