You are overlooking the pollution the emit while running, which is considerable, especially 2-stroke ones. A gas leaf blower used for an hour emits the same air pollution as driving 1,100 miles (source).

And the fact that that oil has to be changed periodically. They also have many plastic parts AND small engines have a notoriously high failure rate when used with ethanol fuels.

Meanwhile, the electric motors in battery ones basically run forever and properly cared for the batteries last many years, after which they can be recycled.