Waiting for what?

Your answer has already been very eloquently stated by another user.

Primarily being.... you don't have to get high by drinking alcohol.

The only reason anyone smokes marijuana is to get high. In fact most regular pot users go out of their way to amplify the effects of marijuana by smoking it in bongs or through things like carburetors.

The only real comparison between the two is that both are gateway drugs, especially if usage is started early in age.