Because adjusting the valves on a BR600 isn't something that most people bother with until there's a problem. And it's like a 15 minute job. And that's all there is. There isn't any other "nonsense" to worry about. They start up nice and easy and they run and run and run. They're lightweight compared to the competition and they have plenty of power for 99% of the users. They are literally all I see here in Greenville. You may on a rare ocassion see a Echo but that's about it.
They also have some features that other blowers don't, like a length adjustable blowing tube and adjustments for cold weather use.