Why? The reasons vary from case to case: the menu package, the commercial venue and, of course, the publicity. Historically, there were other reasons too: in 2004, when the "mad cow" incident stopped for a while the beef imports from USA, the fans of the Yoshinoya chain made huge queues in front of their favorite restaurants for a last meal...
I never had the patience to wait in line to a restaurant queue, not even for a few minutes, let alone for a long queue like the one in this photo, taken in Nankinmachi, Kobe China Town.
EXIF info:
Nikon D300
Lens: 8-16mm F/4.5-5.6G
Focal Length: 8mm
Aperture: F/7.1
Shutter Speed: 1/800s
ISO Sensitivity: ISO 250