I did not think of this. It's elaborated from a friend's insight, which I helped induce.
Viruses invade an organism, and hijack some of its resources towards making copies of the virus. The virus does nothing interesting on its own and is not clearly alive. Yet they end up being common sith the invaded organisms enable their proliferation.
Clothing is worn by humans, and some humans make more clothing. The clothing does nothing interesting on its own (except be passively present and visible) and is clearly not alive. Yet it ends up common sith humans make more of it.
See the equivalence?
It's an equivalence that, being incomplete, people usually ignore. The main difference that makes viruses kinda-alive is that viruses specifically induce their own reproduction, whereas humans decide to make clothing uninfluenced by the clothing — or so it would seem.
We could equally well make the same comparison to viruses for just about any artifical product. It's more accurate in the case of clothing, and even more so when you distinguish different "species" thereof, for the presence of such an item "infecting" people helps to induce its demand and hence production.
If you don't distinguish "species" so closely, shoes (the original target of this observation) may be the most acutely viral: their frequent use and production is specific to a culture, not universal, and as such is self-sustaining, dependent on this positive feedback loop.