That's a good observation. Making a quieter leaf blower by greatly reducing its output is pretty easy. But the professional landscaping crews getting paid by the hour won't choose a tool that makes their job take 5x as long.
Random thought: Would it be beneficial if residentially-annoying equipment was required to fall into certain standard frequency/harmonic pprofiles? Would that make it easier and cheaper to design absorptive or anti-noise measures?
In other words, a world where you could buy super-cheap earbuds guaranteed to nullify all leaf blowers.
Figure out what ranges of sound are attenuated well by foliage, siding, wall insulation, gypsum board. Though it’s probably windows most of the sound comes through so what frequencies are lowered by double pane windows.