Ugh. This again. Couple things.

(1) The Israelis first adopted the hammer-down carry method because of the limitations of their equipment. Remember, the Israelis got dumped into unfriendly country, and weren't given much help. They pretty much took whatever arms they could get. That meant that their pistols weren't standardized. Literally whatever junk got donated to them.

How do you train a bunch of guys to carry a bunch of non-standardized semiautomatic pistols, in various states of working order, of virtually all mechanisms and actions? Hammer down on an empty chamber. It allows for safe carry of any handgun, no matter the design, even if it's some piece of trash with half a hammer hook and a busted thumb safety.

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(2) The most popular way for a Palestinian troublemaker to get a hold of a weapon is to steal it from an Israeli on the street. Remember, the Israelis also have to share sidewalks with their enemies.

What's the first thing said Palestinian does with his new sidearm? He shoots the guy that he stole it off of.

Carrying with a hammer down on an empty chamber makes drawing and firing take longer for both sides. Hence, you've got more time to react to having your gun snatched.

American police have done the same thing in different ways. On guns with magazine disconnects, popping the mag catch either during a struggle for the gun, or when transporting prisoners, was standard training for a while.

Now, combine #1 with #2, and you have your answer as for why.

All that said, for the competent American CCW carrier, empty chambers make no bloody sense whatsoever.