Logging is something that is necessary but is (relatively) rarely used. As such it can be made much more compact in terms of storage.
For example the data most commonly logged like ip, date, time and other data that can be represented as an integer is being stored as text.
If logging was stored as binary data, a lot of space could be preserved thus requiring less rotation and increasing disk lifespan, especially with SSDs where writes are limited.
Some may say that it is such a minor issue that it does not really matter, but taking in consideration the effort needed to build such mechanism it makes no sense not to. Anyone can make this for like two days in his spare time, why don't people do this?