I would also suggest weight would be a very large issue. Water is (obviously) incompressible unlike halon and would require a large storage tank.
I have had experience with hi-fog systems (I believe that is just a trade name) when working at sea and even allowing for scale and space available on ship they took up a fair bit of space. The installations tended to be manually activated with guarded activation points inside and outside machinery spaces. They are very effective - on training courses I was shown videos of actual fires where the systems had been used and they knocked the fire out very quickly.
On a ship or fixed installation where weight is not a massive marginal issue they are clearly an easy engineering choice; they also have the massive advantage over (for example) CO2 systems of being survivable if personnel are in the compartments when activated. I suspect for aviation applications weight and electrical interference are the two primary drawbacks.