When you wash the car, do you ever use any kind of chemical or solvent while wiping down the dashboard? (Or if you have someone else wash the car, do you know what they use to spray their rags?)
That's not wearing thin from abrasion/normal rubbing (to witness that, look at a soft touch painted mouse or cell phone after a few years) it appears that some type of oil or residue has gotten under those keys via the open area (number) and started to seep behind which is causing the paint to shrink back.
Do you have a significant other, child, guest who ever wears any hand lotions?
Otherwise do you wipe the buttons down with any type of off the shelf cleaner when detailing the car?
Either of those would be my guest - I design products with soft touch paint and this is exactly the type of failure you see after exposure to any type of oleic acid or alcohol. I see you're in Australia too so the extreme heat the car may see may also be part of the issue.
Current: '15 M235i Vert
Previous: '13 335i, '08 TL-S, '00 Corvette