To be fair and to the extent of my knowledge, what LND calls backup is more like an emergency recover which can fail since your peers need to cooperate with you to recover your funds.

Maybe someone else can expand on this, it’s been some time since I last read about this.

update: I’m talking about SCB as explained here. I read some controversy around naming it backups since it’s not a backup in the common sense where you can recover from failure without any third party interaction required.