It exists because HTTP is not a good replacement for it.

It's especially mediocre when you want to download/upload multiple files like a directory with many files inside of it.

A friend recently shared with me his file collection, through OwnCloud. It was such a pain to download. Each file is a separate link. I can't use wget to pull it, because of authentication. It had some cli tools, but it was buggy and couldn't make it work. And of course no ftp. Essentially it forced me to click every single file. I couldn't even verify the files downloaded correctly.

FTP is actually great for what it does and with clients like lftp it's fairly enjoyable to use. If you want to kill it, better make a worthy alternative.