USB isn’t just storage, it’s way more than that. If you plug a USB stick into your computer you have no way of knowing beforehand what the device actually is or what it does. Is the device a normal USB flash drive? Or is it actually something far more malicious?

There are USB sticks, in the wild, which impersonate a keyboard. When connected to a computer, at some point, they will send keyboard commands to the computer in an attempt to fire up PowerShell and run commands that install malware.

In general, you should not use a USB stick unless you know its provenance. Consider them highly dangerous. Be especially suspicious of USB sticks that you find “lost” near your business, since somebody may be targeting your business—this is a common technique both for pentesters and for actual criminals.

USBs usually have a CPU inside that sits between the storage and PC. This way the PC doesn't need to know a thing about the storage and the CPU can do whatever it needs to implement the USB protocol. However the CPU can be malicious and modify files

USB is way more than storage. No floppy disk keyboards exist.