When you want to transfer data between computers you need a program to send the data and the other computer needs a program to receive the data. These programs need to understand each other. FTP is a protocol, an agreement about format and commands, that will be used by sender & receiver. FTP is here to stay, although more & more you’ll be using SFTP, using a secure channel. It was designed by and for use with unix like file systems, which have a directory structure imposed on the storage device. ie the hard disk has directories within directories and at the bottom are the files.
Amazon adopted a different scheme for its AWS cloud storage. Cloud storage is not like having a specific device, like a hard drive, to hold files, its like having millions of drives, or equivalent solid state memory or any other technology looking like a vast storage space. There are no devices or directories. There are buckets holding files. Commonly the file name looks like a directory path, but all those slashes are just characters in the longish file name. A protocol (agreement about format and commands) to efficiently access this kind of storage is used, DreamHost uses the AWS protocol for DreamObjects.