I'm not sure but antipsychotics are the only effective treatment for delusions etc that I know of but they seem to take a lot longer to work than for hallucinations so I'm not sure its actually the dopamine inhibition as a direct thing. The whole pathway is complex because even for the case of hallucinations you can have a lower level of NMDAR signalling but blockade of D2 receptors can increase levels of expression of NMDAR correcting that problem which has nothing to do with levels of endogenous dopamine being too high or too low. So targeting a particular molecule in the cell doesn't actually mean that its the actual cause. In some cases though there clearly is too much dopamine like after taking street drugs like cocaine/amphetamine and antipsychotics work on that too through direct dopamine blockade. One argument that's been made is that the drugs have sort of an epigenetic effect leading to changes in gene methylation and transcription which changes multiple genes at once. The short answer is we have no idea why any of this happens----there are lots of models but there is only one class of drugs that works for this stuff right now(antipsychotics) so it almost doesn't matter what the underlying mechanism is. Basically you pick a drug based on side effect tolerability and effectiveness rather than any sort of actual mechanistic reason.