>can't any money transferred just be sent back by the banks by editing the ledgers?

No, traditional western finance isn't like a unified database, but rather many controlled by different parties in different countries. In theory you could write it back, but it's closer to bittorrent - if someone downloads a song from you then you can't just take it back.

Some stuff can be voided and there are clearing house mechanisms but if money moves fast enough across enough borders then getting it back is near impossible