Because these are cryptographic primitives and you're supposed to be educated enough for using them correctly. If you do not want to think about that, use a hi

Because these are cryptographic primitives and you're supposed to be educated enough for using them correctly. If you do not want to think about that, use a higher-level cryptographic libraries that make all these decisions for you: how IV is generated, how it is stored together with the ciphertext, how do you compute authentication token, how to you compute the encryption key, what algorithm you use, etc.