So if I monitor a profile that was last active more than 3 days ago, and it's status switches to "(Recently)", I know it's became active right at that moment.
Yes but you see, now it requires more resources to monitor each user's activity status, since the web server is no longer giving handouts.
For example, if BPIP were to now scrape all ~4 million profiles and filter the ones with a (Recently) date, then it can only assume the login came from the last 72 hours, unless it has previously scraped an actual date which it can use as a reference point. The independent-/calculated "last active" time becomes fuzzy as a result.