I think one big difference is that the SOPA campaign had a very clear-cut goal of stopping that legislation while this campaign is "against mass surveillance" which is much more nebulous. Most people on the Internet seem to agree that they are against mass surveillance, but there is a lack of clear goals and demands that everyone can get behind.
Worse, they all have different levels of acceptable surveillance. Many Americans think that the current spying is ok, many more think spying on all non-Americans is ok, many other Americans thing ANY spying is bad.
The vast majority of Americans could recognize that SOPA was just plain bad: bad for business, bad for users, bad for everybody.
