Cause they used 60's era Patton tanks as Tigers and showed them driving across desert landscape. Last time I looked, "the Ardennes is a thick forest!!
Ah yes the scorched desert of Belgium! It was filmed in Spain. Maybe it was all Clint Eastwoods fault. Interesting article about Eisenhower denouncing the movie. Apparently there had been another planned movie about the battle where Patton was gonna be played by John Wayne. That I would have paid to see.
Sorry forgot to mention the article is on the IMDB site.