This is true of all table games, not just craps. The policy against coloring up, except when leaving, comes down from management, so don’t blame the dealers. A good dealer is supposed to keep the player well armed with chips at the level he is betting. Coloring up goes against this purpose. It will lead to chip shortages, causing the player to ask to break down the big chips, which wastes time. There may also be an unstated purpose that the player will be unlikely to bet the big chip.