Why didn’t Johnny Sack just have Ralph killed quietly?

Ego.

Trust me you don't draw attention when you want to do something....not good.

He needed to get permission to kill Ralph. Which means he needs to tell people what happened and in order to convince them that it was an offense worthy of death, he needed to make a big deal out of it.

Johnny thought he could leverage Ralph's indiscretions against the entire New Jersey crew as he felt that the Esplanade project was not bringing him enough money. He was driven by greed and he thought his indignation over the insult would benefit him in the long run. It backfired.

Its a plot hole

Despite his outward fury, he knew that killing him was out of bounds.

Another situation that Tony handled poorly.

The sopranos made light of killing a made guy, it happened too much, REAL mobsters like micheal franzese have always said that you wouldn't even raise your voice to an another made man. it's not something that is done as much as the movies make out.

But anyway, johnny sack was going around telling everyone and anyone that he wanted to whack ralph because of the joke he made about ginny, so imagine that ralph just happens to turn up dead or not turn up at all, would be some coincidence eh? it would be obvious.

It depends what logic and reasoning you want to use, real life or sopranosworld? in the real world if even the underboss of a NY family killed a made man when the boss said no (like carmine snr told him) he'd be dead.

Johnny hired someone to whack ralphie in florida, then changed his mind, when he saw ginny stuffing her face, before that he said "i'll deal with the fall out" it would have been interesting to see how that played out if he had killed ralph.

It was difficult problem, because an underboss like johnny shouldn't have to accept a joke like that, but carmine snr knew that ralphie was a huge money maker with the esplanade. tony later said "carmine never made that right with johnny"

In the sopranos he might have got away with it, it wasn't very realistic at times.

in the real world, Johnnys funeral would have been the day after ralphies without a YES from the boss.