I have two answers for you:

1. All that AI really does is a (partially) randomized exploration of the space that has been spanned by existing music. AI creativity, as far as it can be said to exist, is limited by this. You, on the other hand, are human and not bound by any of these limitations. You are free to explore wild things that no AI can do. Just as a completely random example, you could go out, record noises your environment (even if it's just with the smartphone), grab interesting parts, chop them up, process them and turn them into unique new instruments. Bang on random stuff that has a nice ring to it. Record background hums, apply filters and envelopes to them etc. And there are so many other ways to produce unique creations.

2. Most importantly, music is a form of human expression. It is able to capture the human condition in a unique way. As a human, you can express these things genuinely through your own emotions, experiences, memories etc. AI systems can only produce hollow facsimiles of this. Regardless of whether you are conscious about it, every piece of music that you create is a reflection of you: your thoughts, your emotions, your process. And that imparts the true value on your creations.