Stskeeps has it.

It's partially about what people want to see more or less of (e.g., on-topic stuff about Maemo is desirable, random stuff about summer cabins, postal carriers, or even other Linux distros is not) and partially about opinion (e.g., ThoughtFix's post about a more Canola-like UI is on-topic, but many people don't like the idea, so thumb it down).

Arguably, some of the first stems from ignorance (people may not realize Midgard is what runs maemo.org, or that GUPnP is an important part of Fremantle), and some of the second is sometimes more vindictive than anything else.

People will heart or thumb what they will for the reasons they choose, which is why we don't leave it up to just one person. In the end, interesting, on-topic stuff goes to the front page, off-topic and uninteresting stuff doesn't.

So, make Planet more fair, don't forget to rate the articles!