If someone pushes you, and you start swinging your arms wildly to balance yourself, but end up falling in a different direction - why did you fall?
Lots of close contact will mean you're far less likely to panic in a fight situation. Most people have never been in a fight let alone hit.
Plus the fitness of course. Judo helps enormously with core strength.
BJJ borrows a lot from Judo, particularly the grappling.