The thing is, our brain is the most complex thing of the human body.
People often prefer to use the "neurodivergent" word because you might have way more things than just autism, you might even have some undocumented disorders, it's just hard to be specific when come to this.
It's like trying to give a unique name to a mix of vegetables and etc... So people just came up with the world "salad".
I personally prefer neurodivergent because I admit, not even myself, and maybe not even an specialist would be able to diagnose everything that happens in my brain. But we all know it must be something related to neurons.