There is on average a new submission every minute on HN. So basically an entry exposure in /newest first page is 30 minutes.

How many real people actually visit this page, browse submission, let alone consult the links, vote in earnest vs bot manipulation? Being on the front page of HN is valuable.

You can't downvote submission (or at least I can't) so low quality posts score can't even really be corrected (except flagging I guess, which sometimes feels abused but that's another problem).