It was harder to define and lock down to a slick process. There is a reply further up to a different question which explains it in terms of variance.

https://news.ycombinator.com/item?id=8696134

Some platforms have seen a lot of success from doing something limited and simple really well (Instagram, Twitter, etc) rather than trying to be a tool for everything. Maybe that's a parallel?

I think lack of growth is a more accurate issue. TaskRabbit wasn't in the business it wanted to be in - they were a matchmaker not a middleman, and match making only turns a profit at huge scales - dating is pretty much the entire human race, so they can only go downhill from that opportunity.