The message
from Edward W. Thompson contains these words:

The critical comment by respondent that wire nuts are not 'airtight' I
find puzzling. Of course they are not and neither are any normal
electrical connections made by other means.

I suspect the important bit is that the pressure at the points of
contact isn't high enough to preclude air getting in between the
conductors which is a well known and serious problem. The conductor gets
warm and oxidises nicely, leading to a higher impedance and so on.

A proper high pressure gas tight connection forces the conductors
together hard enough so that they're deformed and no air can get between
the mating faces. This stops the problem at source.

From the few wirenuts that I've met they couldn't possible achieve the
sort of clamping pressure that a screw terminal in a junction box could
and as a result lack the reliability.

--
Skipweasel
Pay no attention to that man behind the curtain.