You expect a file transfer program to reliably and faithfully transfer your files, byte-for-byte, from one system to another. FTP spits in your face and shits on your chest. You know how Linux uses LF (i.e. \n) for newlines and Windows uses CRLF (i.e. \r\n) for newlines? Pretty annoying, right? Well, FTP's ASCII mode will automatically rip off those \r characters for you! Sounds pretty sweet, right? Fuck no it's not. All of the sudden, your file checksums have changed. If you pass the same file back to a Windows user with a different and more sane file transfer system, then they get a broken file because FTP didn't mind its own fucking business. If you have a CRLF file and need an LF file, just explicitly use dos2unix. Wanna go the other way? unix2dos. The tool has been around since 1989 and it's great.
Now, what if you're not transferring text, but instead are transferring a picture of a cute cat? What if your binary data happens to have 0x0D0x0A somewhere in it? Well, ASCII mode will happily translate that to 0x0A and fucking ruin your adorable cat picture that you were going to share with your depressed significant other in an attempt to cheer them up. Now the ruined JPEG will remind them of the futility of their situation and they'll slide even deeper into cold emptiness. Thanks, FTP.
You can tell your client to use binary mode and this problem goes away! In fact, modern clients do this automatically so your SO gets to see the adorable fuzzy cat picture. But let's just stop and think about this. Why use a protocol that is dangerous by default? Why use a protocol that supports no form of security (unless you're using fucking godawful FTPS or FTP over SSH)? Why use a protocol that is so broken by design that small business hardware has been designed to try to unfuck it? Is it faster? I mean, not really. SFTP has encryption/decryption overhead, but your CPU is so fast that you'd need to transfer at 25+ Gb/s to notice it. Is it easier? Fuck no it's not easier, look at all of the stupid footguns I've just mentioned. Is it simpler? The line protocol is simple, but so is HTTP, and HTTP has a much simpler control flow path (merging the data and control planes is objectively the right thing to do in this context). And shit, you want a simple protocol for cases where you don't have a lot of CPU power? Use fucking TFTP. It's dogshit, but it was intentionally designed to be dogshit so that a fucking potato could receive data with it.
There is no task that is currently being done with FTP that couldn't be done more easily, more securely, and more quickly with some other protocol (like fucking SSH and SFTP, which is now built into fucking Windows for god's sake). Fuck FTP.