Because hundreds of thousands of refilled or remanufactured ink cartridges are printing daily in all corners of the world. In other words, the law requiring to use original only inkjet cartridges is honored more in the breach than in the observance. A remanufactured ink cartridge is an inkjet cartridge refilled via an industrial process and delivered to perform as new. If the test is passed, the inkjet cartridge is cleaned, flushed through a flushing machine and readied for refilling. The ink cartridge is refilled, tested for proper operation and weighed.
Weight is a measure that the proper volume of inkjet ink has been injected.
The ink cartridge is packed for shipping. No on two grounds. User is NOT obliged to utilize supplies furnished by the original manufacturer, to maintain the warranty. There are limits here too if the manufacturer can prove that the supplies do not comply with the standards required by the original equipment then he can refuse to honor the warranty. But this is impossible.