Spammers are possibly trying to take advantage of npmjs.com domain's high Google rank. I found and reported this spam account [1] with links to download movies. They seem to be using npmjs as a free web host with good SEO. [1] https://www.npmjs.com/~aarilzd
If the spammers only want to be indexed, then NPM should disable indexing for major search engines. But still allow it to be indexed other ways, which aren't unearthed on Google search. Other ideas include: do not index new packages before they've garnered enough downloads.
Especially cran because it has pretty rigorous entry requirements so being in cran is a signal of at least some minimal quality.