Nit: no ML is deterministic in any way. Anything that is Generative AI is ML. This fact is literally built into the algorithms at the mathematical level.
First, they all add a source of randomness, and second deterministic according to the users model. A pseudo-random number generator is also deterministic in the technical sense, but for the user it isn't.
When the user can't reason about it, it isn't deterministic to them.
When the user can't reason about it, it isn't deterministic to them.