If I look at the data here on MSEdata here on MSE (10K only), I see that since the start of 2021 17 questions have been migrated away from MSE. That would boil down to no more than 80 questions a year.
Since March 25th over 45 questions have been deleted. That is more than 10 per day, or over 3,5K per year, or 45x times more often than a migration.
So yeah, migration is an exceptional circumstance.