Well, there are - CIEMs, most BA IEMs, Shure SE215, Logitech/Ultimate Ears UE200, Etymotic ER-4 series, ...
The key is just that one inserts them slowly and takes them out slowly (while simultaneously breaking the seal) as well in order to avoid physical damage of the ear drums.
Especially with deep fitting IEMs, a careful hand is required, as the seal is much deeper and stronger than with normal fully closed IEMs that have a "short" nozzle that usually seals before the first bend of the ear canal.
That must be horrible... I mean... Really horrible.
Imagine how one mistake, one wrong movement could break the ear drum, or leave bad hearing damage in that case.
I imagines they have very small vent that would equalize the pressure. Imagining they would have absolutely no vents, is painful to imagine how they go inside.
I've never had a IEM without holes in it. Am quite happy with it this way. Would not want a IEM that can break my hearing, like if, say, I wrongfully get the cable and they are forced out of ears, thing that can happen while staying at desk and just browsing and doing a more brutal movement of mouse
I've been pondering the same thing now that I'm using an authentic pair valued at $999 Canadian and not my $50 Chinese copy...not strictly pocket change as we say.
Oh, those are the right questions
It seems that for most people, ie800 is fine to be taken outside.
I was most concerned about dust particles, air humidity, and heat / sun. Romanian summers are awful. 40 degrees Celsius on shade. imagine the temperature under direct sun light.
I would also avoid exposure to cigarette smoke. Cigarette leaves a film on any surface, a slimy yellow-gray film made out of some fat acids, that can thicken the membrane, and affect the SQ severely.
This is something to be avoided on any IEM / headphone. Cigarette smoke will destroy anything, even circuits, because that film is electrically conductive.