Why no 9?

My phone (not cell phone, a cordless phone), which is somewhat high-tech, has a speaker setting which I use frequently. I like it. It's good. It's clear. It does the job.

However, I have one gripe. I go to increase the volume as my printer hammers out my plans, and I notice three beeps when I hit volume level 8. It goes no higher. Why not 9 or 10? Why stop at 8? 8 is plenty loud, but to 9, at least.