I think there are three reasons Godwin's Law has been successful. The first two are that it's easy to apply and necessary. It's hard to tell if something is an argumentum ad hominem (aka "personal attack") or a legitimate challenge to someone's credentials or style, and some level of argumentum ad hominem is almost necessary when confronting trolls. But argumentum ad hitlerums are always obvious and rarely good.
The third reason for its success is that it's funny. Before everyone and their brother had heard of Godwin's Law, you could always get a laugh and look particularly witty by bringing it up if an opponent made a Nazi analogy. There was every incentive for people to spread it across the internet.
I think the more Godwin's Law type norms we spread, the better. So I would like to publicize one I found recently that I really, really like. It's called the argumentum ad cellarium. According to RationalWiki:
An argumentum ad cellarium is a variety of ad hominem attack sometimes found in debates and comments on the internet. The argument is used to dismiss someone or their views by accusing them of lacking in the usual social and living skills that society expects, and thus being forced to resort to living in their parents' basement.
I see this a whole lot more than Nazi analogies nowadays, and it ticks the same boxes of being offensive, symptomatic of poor debate, and almost inevitably derailing the argument in which it occurs.
I propose two new laws. First, and named after the user who wrote the argumentum ad cellarium article, Martin's Law: If during an online argument anyone accuses their interlocutor of living in their parents' basement, the argument is over and the accuser has lost.
Second, Martin's Law, Reflexive Corollary: If during an online argument anyone accuses their interlocutor of living in their parents' basement, the accuser has identified themselves as exactly the sort of internet troll who may well live in their parents' basement.
Conjectures that a person doesn't have a girlfriend, doesn't shower, or has acne - based solely on the position they take in an argument - are all variants of the argumentum ad cellarium and Martin's Law should equally apply.