Charles Ellicott Commentary Matthew 13:6

"and when the sun was risen, they were scorched; and because they had no root, they withered away." — Matthew 13:6 (ASV)

Because they had no root—or, as in Luke 8:6, because they lacked moisture. The growth had been overly rapid, and the presence of the underlying rock at once made the heat more intense and deprived the plant of the conditions for resistance.