One of those reasons is there are a lot of unbelievable and ridiculous scenarios such as the mailman just barely missing romeo causing them to both die in the long run. Another example of an unrealistic scenario is when juliet wakes up a second to late causing romeo to drink the poison. The last ridiculous and totally unbelievable scenario in romeo and juliet is when juliet kills herself simply because romeo died.
My last point towards how romeo and juliet could be considered a comedy and not a tragedy is that it could be a comical farce of the typical tragedy. For example when they get married almost the day after they met even though they were only around the age of 14. Also how they will do the stupidest things for love such as committing suicide and doing illegal things just for something as simple as saying hi to each