A general purpose computing device is unavoidable, it's exceedingly difficult to build anything close to it. Encrypted storage is trivial without dedicated hardware, using open, validated software solutions. Even better, if bugs or backdoors are found you don't need to throw out your encrypted stick, just update the software or reencrypt.

Because what I said above might sound like black magic to anyone who knows nothing about the topic I will expand.

The CPU on which the software runs gets far more scrutiny than the obscure encryption engine on the USB stick. And it's possible to validate the software encryption with minimal effort. Verify the output with various software implementations of the same algorithm, ran on different CPUs. They have to be compatible and can't all have the same bug or backdoor.

An encrypted stick is impossible to validate by the end user. They have no access to the CPU encryption engine or the raw storage so can't know the algorithm implementation, or the output to disk format which is probably proprietary.