I noticed this immediately upon upgrading from a 2014 MBP to the M1 MBA, probably because I am very specific about the cleanliness of touch-points, such as keyboards, mouse, steering wheels, etc. Needless to say, it isn't my hands; I don't use any lotions or oily products, and wash my hands constantly. It seems like the new keys pick up and retain dirt and oil more easily. Luckily, my MBA spends most of the time connected to an external monitor and keyboard/mouse, but the shiny keys became apparent on a week-long trip with just the laptop.
Approximately 2 months ago, I received a new HP Elitebook for work. Even though I use it like an actual laptop, moving around constantly, typing and using the trackpad, there are no signs of wear except for a slightly glossier area on the trackpad (which looks more like residual dirt/oil, and not actual damage to the material). The difference between the HP and the MBA keyboard wear is night and day. I really wish they'd go back to the old plastic that wasn't as susceptible to such minor wear.