Etymology

Because it is a wall and is located at the front of the court.

Noun

front wall (plural front walls)Category:English lemmas#FRONTWALLCategory:English nouns#FRONTWALLCategory:English countable nouns#FRONTWALLCategory:English multiword terms#FRONTWALLCategory:English entries with incorrect language header#FRONTWALLCategory:Pages with entries#FRONT%20WALLCategory:Pages with 1 entry#FRONT%20WALL

1. (squashCategory:en:Squash#FRONTWALL, racquetball) The main and largest wall in court, located at the front of the world; the wall which the ball must hit in a rally.
2. Used other than figuratively or idiomatically: see front,‎ wall.