Rooms homes can be very dusty environments don't kidd you're self thinking you're home is clean, no such thing unless its "White Room".
Look at a typical keyboard and run a small piece of cardboard though the keys and see how much skin hairs dust that has built up in just a few months.
Hands rubbing hands small particles of skin will losen and fall between the keys even fingers against the keys.
Head rubbing head hairs fall off and get between the keys
Cloths rubbing clothing small particles of cloth fibers and hairs and skin on cloths all this will find its way between a typical common keyboard.
I looked around after thinking does such a flat keyboard exits and I found one of many but the prices are way too expensive to type typical common text each second. I think I can wait until they are within common peoples budgets £50.00 or lower. Not spending out £150 or higher for keyboard.
If it gets wet at least it won't multiple like Gremlins.
And common keyboards often get wet and sticky with keys getting stiff.