A simple voltage divider problem
Your meter needs current to make a measurement. The objective is for your meter to sink or source so little current compared to the circuit that it does not significantly affect what is being measured. This lets you approximate the current from your meter as zero. It's the whole quantum mechanics thing where you can't observe/measure something without somehow influencing that thing thus disturbing the original state that you were trying to measure.

But if the current that the meter sinks/sources is truly zero (or below that required by the meter itself which, in a way is determined by how high an input impedance it is relative to what you are measuring so that it has minimal effect as stated by @jonk in the comments. The air resistance is so high compared to the meeter input impedance the meter is like a short circuit across the air), then your meter can't sink/source this current, then no measurement.