First time for the crossover (April 2019) was about 10 weeks before the release of Shadowbringers.

Second time for the crossover (Sept 2021) was about 10 weeks before the release of Endwalker.

Maybe the third time will be about 10 weeks before the release of 7.0? The timing on the first two was probably coincidence but someone in SE might have picked up on it as amusing and decided to turn it into a recurring thing.