Its a feedback loop, they make it to the front page, the submitter thus gets a bit of karma, so other folks hunt around and submit stories they think are cool. If you plot front page stories over time you can see this effect in action. If the topic is interesting to you, its "cool" and if the topic is not interesting its "annoying" :-)

I suspect its karma building posts.

I noticed the phenomena when an off topic post gets popular real quick and makes the FP, other related stories quickly get posted.

Not that there is anything wrong with it, its just something I’ve noticed.

EDIT: Just saw ChuckMcM's post. Didn't mean to be redundant, but I'll leave it here anyways.

it's a prelude for hn for aviation, coming up soon.