Often pinball machines sit with credits on and their Start button flashing ready to play because winning a free game of pinball is a concept utterly alien to most people
Other games in the arcade don't let you play for free
Hell Mario Kart takes your dollar and you play one race and then it's game over even if you came in first position, meanwhile pinball's over here all HEY YOU GOT ENOUGH POINTS TO WIN A REPLAY, or HEY YOU SUCK AT PINBALL BUT THE LAST TWO DIGITS OF YOUR SCORE RANDOMLY MATCHED THIS NUMBER SO HAVE A REPLAY
For a couple of years in the 90's Williams tried having the machines scream "FREE GAME" instead of "Replay" but there was too much Everybody Knows for that to catch on