One justification I hear is that if the disbelievers were to stay alive on the earth forever they won't believe meaning their sin is infinite and thus their punishment should be infinite too. but even if they were not to believe if they stayed on the earth forever, they still died, and since they died, they're being punished for a sin they haven't committed which is eternal hell, which I believe is unfair.
Another problem with this justification is that it contradicts one Muslim answer for the question "why did god leave us to live on earth instead of judging us instantly into heaven or hell" which is "God left us on earth to be witnesses on our actions so that we can't deny them when we're being judged and have no excuse for our sins". The contradiction happens because the disbelievers will be accounted and tormented for a sin that they were not witnesses of.