To be fair, for every well behaved background app (ie. a ssh server that's listening on a socket, which should consume basically zero power), there's probably 10 other misbehaving app that's phoning home every 30 seconds for ad/tracking/analytics purposes. Moreover, "battery life" is a metric that often shows up on reviews, so it makes sense to game this metric as hard as possible, especially since most people probably aren't running servers 24/7 on their phones.