I wouldn't say it's one leading into the other. It's the same root cause for both. They were really socially awkward and lacked self confidence growing up, which led to them developing the complex that caused them to become nice guys, and also caused them to retreat into the escapism of anime.
There are a couple of reasons these guys are far more prevalent now than in the days of yesteryear. The workforce has mostly moved to jobs that require more social skills making them less employable and financially solvent, less women are looking to get married or get into a relationship, and there's an endless flood of escapism for them to hide in instead of facing their problems leading to them not kicking their own asses and growing some balls to fix their problems.
The option of them accepting their lower status and settling for a fat or ugly chick is also a route they refuse to take because porn has desensitized them to the point where they cannot get sexually aroused to such women.