Why did Jesus frequently warn that people in Hell will be gnashing their teeth and weeping?

Because of His great love for us... God is not willing that any should perish... And Jesus died so that all could be saved... But God did not make robots. Each person has the choice to serve Him or reject Him. Those who choose to reject Him will live forever away from Him. Separation from the Source of all that is Good, Satisfying, and Loving sounds intensely miserable to me. Thanks for sharing and warning people about the Truth!