Engineering, manufacturing, packaging, and retailing a $39 hydraulic jack can have its pitfalls. Say you have a run of 50,000 jacks and a few of them start dropping cars on people. What would happen to the small amount of profit you made on this deal? It would not take long before the consumer product safety group or some other group to step in and stop the sale of this product, which means all stores, Kmart, Sears, Harbor Freight, etc. sends back what unsold product they have left for a refund, not to mention a likely recall, so that any sold jacks can be returned for a full refund. The above action is pretty much the death, or at least a very big hit to any company.
Can a jack fail? Sure it can. Ive used hydraulic jacks most my life and as others have said, they ALL state in the instructions to always use a jack stand in combination. I became so tired of dragging 60 lbs jacks around the garage, that I installed a lift. Much safer, easier on my back, and no more rolling around on a creeper. Use all tools in the manner for which they were designed paying heed to the cautions and warnings and you should rarely to never have a problem.