It's all money. A good charger will have protection; but there's also extra protection in the device itself for balancing the cells. All of these things cost extra to manufacture.

There's also things that no amount of electronic protection can save you from...like water; physical damage of a cell; or just a badly-manufactured cell. Lithium cells are prone to thermal runaway which is scientese for saying they're really, really bad at dealing with short-circuits.