Why is SN1 mechanism followed in diazo aromatic compounds' nucleophilic substitution?

There is considerable [evidence](https://chemistry.stackexchange.com/questions/84603/what-is-the-reaction-mechanism-of-nitrogen-leaving-from-diazo-compounds/95939#95939) that SN1 mechanism is followed in diazo aromatic compounds' nucleophilic substitution. I would like to know the reason for this and why is it preferred to SNAr mechanism even when the $\ce{N2+}$ could stabilize the carbanion-type intermediate through -I effect.


Does it have to do with the excellent leaving tendency of $\ce{N2+}$ but at the cost of formation of unstable [phenyl cation](https://chemistry.stackexchange.com/questions/10509/why-are-vinylic-and-arylic-carbocations-highly-unstable)? 


