In order to display a non-fluctuating distance remaining number, Tesla would essentially have to either predict the future or vastly under-report the real number. The car doesn't know whether you are stopping for 5 minutes in 20 degree weather or 10 hours, and UX would be even stranger would it attempt to guess for you. It looks like they already under-report to some degree, but under-reporting by 1/2 the remaining distance would seem to me to be much less ideal than the current solution, which is to adapt the number to conditions currently observed.