A chart showing the monthly object in Earth orbit by type shows how the problem of space debris is getting worse.
There are many sources of debris. One source is discarded hardware. Launch vehicle upper stages have been left in orbit after they are spent. Satellites are abandoned at the end of useful life, while spacecraft and mission operations have released items such as separation bolts, lens caps, momentum flywheels, nuclear reactor cores, clamp bands, auxiliary motors, launch vehicle fairings, and adapter shrouds.