It's because hazers produce MUCH smaller, particles that don't really disperse like smoke/fog does, it doesn't result in clouds of smoke, more like a mist that hangs around. It's why its good for laser effects. They normally do this by using an atomiser instead of a heating coil and air pump like smoke machines. It really plays havoc with smoke detectors though. The hazer fluid was oil based too which used to leave residues on things that were probably found to be flammable or pose some sort of respiratory risk too. As I said earlier, a lot has changed in the years since being removed though. Water based fluids, dry ice or co2 based machines produce atmospheric effects these days with basically no fire risk. Lots of alternatives don't have the spread/capacity/volume though and things like the scooby high zone is a VERY BIG SHED. Problem often comes down to coverage and cost because of it, especially in the case of co2 machines. Gas usage really drives the operating cost up and im just not sure it's something they are prepared to spend big on. The same thing could be said for wild west falls. You could return the dynamite fuses and explosive effects to lift 2 and the top turntable with modern systems, but when you combine ultra high levels of safety + effects, you really need to spend some decent money on the units to even remotely approach the same effect as real flame/sparks. If you cheap out, it looks like crap. 100% saying it can be done, I'm just not sure there is enough care from upper levels of management when it comes to visuals and theming. Talented staff have come and gone over the last 15-20 years that tried to push the issue, but it's never really gone very far anywhere within the parks. They really should still have electronics and electrical techs specifically dedicated to maintaining theme elements everywhere, thats what AV was for, but it all tends to get lobbed in with Electricians these days. It's not a very high priority if it's not something critical that's stops ride operating or some service/function within a building failing. Spending adequate amounts of money basically fixes 99% of your problems though......