From the traditional signal from a boxer's support staff of throwing such an item into a boxing ring to indicate that the contestant cannot continue the match and is forfeiting to the opponent.
In short, there was so much space and so many things to shove things behind that most people, called on to find a silver cow-creamer there, would have said “Oh, what's the use?” and thrown in the towel.
2024 July 10, Christian Wolmar, “The future of the rail franchises is certainly uncertain”, in RAIL, number 1013, page 50:
One key imponderable is the attitude of the companies that will no longer have a role in the business. It is worth noting here that several have already thrown the towel in or been gently pushed out, such as Stagecoach and National Express.