First, task runners, like templating systems and module bundlers, are easy to write so there are lots of them. Grunt in particular doesn't bring anything to the table that bash scripts don't.
Second, most open-source projects don't make their value prop clear (I learned this the hard way first-hand and I'm still dealing with it) and most people don't have a good rubric to evaluate technologies so they fall back to crappy ones like gzipped size, number of dependencies, or the twitter account of who wrote it. Increasing the level of understanding of performance and how system complexity evolves over time is an important next step for the community to take.
For example I think the excitement around Gulp is legit because the tasks are composed as in-memory streams which is a scalable way to build a performant system. Browserify not so much, since it doesn't bring anything new to the table except maybe that it's so damned easy to use ("philosophy" does not count as bringing something to the table). Webpack, on the other hand is a whole different story since it accepts that static resource packaging (not just single-file JS modularization) is a problem that needs to be tackled holistically and necessitates a certain level of complexity.
I named specific projects not because I have any vested interest in them (I don't really use Gulp for anything) but because I wanted to show concrete examples of how to evaluate technologies on real merit.
Finally, the web frontend community has a huge problem with NIH (not-invented-here) syndrome which is encouraged by npm. For example, there are lots of copycat data binding systems that claim to be "lightweight" or "simple". They're usually written by people that don't know about all of the important edge cases which necessitate certain design decisions or library size. It goes the other way too -- a lot of people are building monolithic app frameworks without doing due diligence on existing systems to see if they can be reused.
If we can slow down and try to respect what others have done and acknowledge what we may not know, I think we can fix this problem.