The muffler in your car weighs a fair bit more than an entire leaf blower. The noise reduction is also aided by enclosing the engine in a compartment with sound deadening, and having 15ft of exhaust piping (and a resonator, and usually multiple catalytic converters). It just can't be done effectively for small engine tools that you have to physically carry around.

2 stroke engines are even worse (chainsaws, weed wackers) because the exhaust has to be tuned for resonance at specific frequencies in order for the engine to make power.

As an owner of some land and many pieces of small engine equipment, I will say that the difference between _no muffler_ and the little mufflers they typically have is still substantial.

The top two reasons are increased cost and increased weight. Far, far down the list is slightly decreased reliability.

We can, but size and weight are important for hand held equipment and so we sacrifice noise and pollution to meet the other requirements.