This is an intuition that many neuroscientists have shared, it's just that direct experimental evidence of 1) it happening at all in a non-trivial way and 2) it being relevant to the behavior of an animal is somewhat scarce.

Plus, the sum and threshold model actually gets you pretty far, as evidenced by artificial neural networks, so there might be some resistance to adding complexity that might not be necessary.

Edit: Google "dendritic computation" if you want to dig deeper.