Besides being the future of world economy, one of the the technical reason is that Bitcoin has inherent problems due to its design, and people feel they can improve on it. For example, Bitcoin transactions have high fees and can take a significant amount of time to process, so some altcoins are designed to have lower fees and faster processing times. The “proof of work” requirement that requires a ridiculous amount of energy usage could be replaced with a different verification method, making the new altcoin more efficient and saving all the world’s energy from being used up to mine Bitcoin.