1) your car will lose max range over it's service life.

2) charging to max range is bad for the battery

3) the rated range isn't the actual range in real life

4) you want to drive 10mph faster

5) cold is hard on EVs

6) wind

7) less availability of charging

8) you don't take it down to 0 miles

All of a sudden, a 400 mile range car is 280 or worse in effective distance.