niftich's got a pretty good answer.

Most social network feeds are organized using machine learning algorithms. The ideal case is to see the latest non-trash content, but that requires the machine to interpret natural language / photos in the post. We're not quite there yet, so instead, algorithms rely on meta-data. I.e. views / shares, and match them to similar character models to yours.

This is one layer removed from the actual content, but in order to assess its entertainment value, it needs context, which takes time to collect. The results in delay in reaching your feed.