It could be a dream schedule timing situation.

You're dream may have ended because your sleep schedule moved out of a REM stage, which is the sleep stage responsible for dreaming. Each time you would try to re-enter the dream, your brain would kick you out, with its own intentions to transition to an NREM sleep stage.

As far as I understand, lucid dreams are limited to the narrow windows in the sleep cycles that are REM stages. Typically, the longest REM stage of the night is up to an hour long, and the shortest is a few minutes. I have a suspicion that the brain can be a little flexible, in that you can enter REM sleep even during a period in the night where normally it would be NREM, but I suspect this flexibility does have its limits, and you may have reached those limits. And my suspicion is just that -- a suspicion.