because if I used their chart which says to measure your foot from tip to ankle then look at the chart to order that size I would have received a pair of sandals that were either too small or too big if I remember correctly, I prefer to know the exact sandal length for the size 40 & 39 .... then I can determine the exact size pair for me. No mistakes, just confirmed measurements.
It's risky buying clothes or shoes of the internet.