Why is it not possible to create a storage solution that protects against ransomware?

Of course, it is possible to do this but it requires considerable cost and diligence. External hardware that only takes data from the target machine, for example - long timeline + key transactions logged. "Backup can't protect against ransomware" statements seem to be just shorthand for "your piece of shit backup doesn't protect against ransomware", which is true but when shortened doesn't seem like the right message.