You make a good point in theory. Unfortunately we’re not able to get accurate info coming from West Africa at the moment and in SL they’re providing families with home care guidelines and “equipment “ as hospitals and clinics have no more room.
I suspect there is something happening statistically allowing periodic exposure by air transmission,...not necessarily airborne.
Like the pig-monkey experiment in Canada a few years back where not all monkeys became infected concurrently, but half of them did acquire the transmission from the isolated piglets, and later the others acquired it, again without fomite or direct contact.
Maybe its a blossoming unencapsulated virions, only happening periodically, infecting some percentage.
When exposed to higher concentrations, such as a corpse of obvious contagious stages, then without PPE infection is near certain without antibodies. Meanwhile, not everybody gets it immediately if temporarily exposed.