"Seems like 'they' would want to keep the chips on the table, since they could be worth a different amount if they were added to a stack at a different table."

I kind of heard the same thing. But they must be used at the same table hence the numbers and letters. Some may argue that it is wrong to harvest roulette chips, but I won't pass judgement. Except that people who harvest them are collectors and not going to re-enter them into a game.
Barry