Over the years they have found alternatives for and phased out most high-explosives used in fireworks. Many high-explosives will just deflagrate/burn but can spontaneously detonate with considerable power if the conditions are right, which makes them dangerous.
Or perhaps the safety improvements are offset by sellers now offering bigger fireworks (either because those are now actually safe and both buyers and sellers are more comfortable with them, or just because of a general hedonic improvement).
Or perhaps they are safer for their users, but worse for starting fires or interfering with low-flying aircraft.
Either way I would be interested in reading more about this, something more nuanced than "fireworks dangerous". At the least it's a counterpoint to what happened with illegal drugs which seem to have become more dangerous as a result of regulation and bans.
There is a parallel in military explosives research. For example, the US military is slowly moving toward “insensitive munitions” which use explosive chemistries that are nearly impossible to detonate accidentally due to fire or impact. This originated in nuclear weapons research but has spread to other weapon systems.
Fireworks are intrinsically dangerous in the hands of incompetence, ignorance, or stupidity. No amount of engineering can solve that problem unfortunately.