Degassing even purified water sample uniformly from site to site would be next to impossible. Also volume is exceedingly difficult to measure accurately and changes rather strongly with temperature. Mass (as weight) doesn’t.
Yes, degassing is difficult, but required. You aren’t talking that everyone is measuring by this.. its the BASE unit you are basing everything else from.. this reference unit is not something used daily.
You deal with the temperature issue by simply adding the requirements of temperature by simply requiring the measurment to be at a certain temperature.
Volume of a known universal liquid should have been the basis of the unit in the first place.