It's a constant fight with nature no matter what you do- damp, mould, leaves/ moss in gutters, weeds, grass growing, hedges growing, fences need maintenance so they don't rot.
No matter how organised and amazing at DIY you are, something is always broken/ in need of replacement or needs updating. Even if against all odds you perform the miracle of having every job done, there is never more than 2 weeks between having all jobs finally done and something going wrong. Taps leak (just fixed the kitchen tap last week, the bathroom tap obviously got jealous and now it has started leaking), appliances break or need regular maintenance (fridge shelf supports are randomly cracking), pipes randomly develop sudden leaks (washing machine pipe had a slow leak into the back of my cupboard that has got missed for weeks), something needs painting or wallpapering (hallway), a carpet or laminate floor somewhere needs replacing (stair runner getting threadbare - not quite a trip hazard yet but give it a few months), a door needs rehanging or the bottom or top planed due to warping (bathroom and living room), a window somewhere will be blown or full of condensation, the bathroom ceiling once again needs a mould treatment as someone living in the house is either unable to use the extractor fan consistently/ the extractor fan needs cleaning as clogged with dust/ the extractor fan actually isn't powerful enough for the power shower you installed despite the plumber buying all the bathroom kit you supposedly need.
As PP said, they are not self cleaning. No matter how many hours a day you dedicate to cleaning, something will always need cleaning. If you have small children (or a man child) then no matter what you do, the house will never be clean. Someone will spill something/ lick something/ smear dirty fingerprints somewhere/ tip toys somewhere.