Did you download the hood from the mfg as a block?
If the software is smart enough to know how high the range hood needs to be, that may be it. However, I doubt if that restriction is hidden in vanila Autocad, maybe in Architecture.
Anyhow, the hood has to be from 26" to 34" above the range top. Most cabinets are 30" above, so it can be flush with the bottom of the cabinets.
Do you have side clearance for the hood?