Need an Audio Engineer to Explain Something

I'm really excited about Apple II computers. The first storage device was cassette tapes. I am trying to reproduce some of the early tapes and I'm a bit confused. The Apple II needs between 2 and 5 volts to read the signal. The tapes I've found have the left channel at -5db and the right at +5db. Obviously Apple knew what they were doing but I'm curious why the data was recorded that way.

I have some technical information here that might help: https://microhertz.io/technical-information