Some brands do it, some don’t. The convenience of having extra blades in the handle is a feature that is hard to do without. Buyers that purchase disposable utility knives don’t need this feature and it won’t factor into their buying decision. There are also no issues with safety by having backup blades in the handle. They are secure, even when the utility knife is dropped. Larger handles typically hold up to five blades in addition to the one being used. When looking at the professional grade utility knives, that number can almost double in size.