Because it’s already able to do almost everything a brain can? State of the art AI models can already learn, reason, communicate, and even create - better than most humans. Using a lot less neurons, and much simpler neuronal structures.
All trends indicate we’re only a couple years away from an AI superintelligence. No additional understanding of biological brains is required to get there.
I remember a similar argument made since the 1980's... 40 years later and a lot of stall-outs...
It could be hubris to assume we know enough yet to replicate our 'kind' of intelligence. Just as it might be hubris to assert AI doesn't have some 'kind' of experience. A minimum (which will be raised once we have a better understanding) is still: change of state, to have an experience - we simply don't know what else exactly is required, so that threshold minimum remains to be raised.
This argument could not be made before March 14 2023, when the first actual AI was released (GPT-4). I remember that day very well because I was extensively testing every GPT model before that (part of my job as an AI researcher). The entire history of human civilization can be separated into before and after that milestone.
We do not need to "replicate" human intelligence. It's enough to "simulate" it. The coming AI models will be entirely "alien" types of intelligence to us, and that's OK as long as they are useful. Most likely these AI models will be able to finally explain to us how our own brains work.
All trends indicate we’re only a couple years away from an AI superintelligence. No additional understanding of biological brains is required to get there.