Ask HN: Why only three filters (newest, news, best) rather than a sliding scale?

I think it would improve HN greatly if one could specify to see the best items from the past n hours/days, rather than just best/news/off. So rather than have best (best from this week-ish), news (best from today-ish) and newest (show all), we could specify a time period, which would show the most upvoted items for the past, e.g. 3 days, or for however long you've been away from HN. I find myself needing the same feature for Reddit all the time. I'm not sure why it must be 3-4 presets, rather than a sliding scale.