Picking up at all confirms that your number is valid, connects, and an adult human at least occasionally answers - this makes your number more valuable for passing on to others.

There isn't much of a peer-to-peer "valid number sharing" market between companies, they protect their lists as a business asset with at least a little value, but larger groups will pass such data around their constituent parts and when a company folds whoever buys their data as a cheap asset is under no obligation to use any do-not-call list as a don-not-call list instead of a real-people-answer-here-add-them-to-the-next-campaign list.