It is possible that human intelligence is not computable, but it looks veeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeery difficult to prove it. Nobody is sure. So the options are:
1) Try to prove that human intelligence is not computable.
2) Give up and go to another research field, like particle physics or artificial sweeteners or whatever.
3) Try to see how close to human intelligence can you get with the current technology. Some small areas may have a good approximation, like image classification, playing chess, …
4) Try to make a fully functional bug compatible human simulation.
For example, currently human intelligence accomplishes much more with much less resource usage (many many orders of magnitude) than any AI algorithm we've developed. Someone could look at the trend, and get an idea of the extent of improvement we'd have to reach parity with human intelligence, and see if it seems at all feasible. A simple quantitative analysis of what we know so far.
At any rate, I'm unaware of any sort of significant effort at #1.
This has been addressed by many authors since modern computation was formulated, for example by Turing himself. We learn about and discuss Newell and Simon's Physical Symbol System hypothesis in undergrad classes, ie. explicitly stating the underlying assumption. Once in a while someone will assert that computation is not sufficient, eg. Penrose, and generate discussion.
In practice you can work on AI-the-engineering-discipline without taking a position on this. Perhaps this is why you feel that researchers don't talk about it. Disciplined scientists tend not to take public positions on things they don't know for sure.
That seems like a pretty uninformed hypothesis. For example, halting oracles can process symbols, but are not computable. So, maybe it is necessary, but easy to show symbol processing may not be sufficient (as I just did).
This has significant implications for the engineering discipline. For example, if the mind is a halting oracle, then you can get much more performant algorithms by incorporating human interaction.
It could be possible that it's computable from a theoretic perspective but not a practical one. After all our biological brains are quite different from our electrical computer chips.
