1) It's stateful, so upgrades also have to upgrade the state (MBs, GBs, TBs of data) 2) It's horrifically high risk because downgrading is usually not a thing

1) It's stateful, so upgrades also have to upgrade the state (MBs, GBs, TBs of data) 2) It's horrifically high risk because downgrading is usually not a thing 3) It usually requires downtime.