Liability and hungry lawyers.
If the location is convenient pedestrians will slip through as they've done before. The sign just makes it harder to play I-sue-the-pants-off-ya game after you've had a close encounter with a forklift tine...
The usual CYA ...
ROFL! I couldn't help but visualize the way my husband drives his forklift (like mario andretti on uppers!), and the way people would scramble out of his way in the plant. If they have a forklift driver like my husband, then "CYA" is NECESSARY!!!
Andria