Why Does an Electric Car’s Estimated Range Drop So Much on the Highway?

My electric car’s displayed range seems reasonably stable around town, then drops quickly during a longer highway drive. The trip is predictable, so the change makes me wonder whether the estimate is reacting to speed, temperature, wind, or something else.

For people who drive EVs regularly, which factors have the biggest effect on highway range, and how useful is the dashboard estimate once you settle into a steady cruising speed? I’m trying to understand what to expect before planning longer trips.