It's a different cycling experience to live in an area with 30+ continuous miles of a paved and forested riverside bike trail and 50+ miles of interlaced dirt trails. Cars can barely be a threat consideration most of the time.
That's fine if you're cycling as a hobby, but if you're cycling as a means of transportation you're going to need to take the roads most of the time. Most of the places you are going to are not going to be next to a forest trail.
It is kind of irritating for a commuter to dismiss competitive and fitness sports as hobbies, but that aside, the aforementioned trail parallels a major highway and it’s used by thousands of cyclists and commuters each day for the majority of their routes. Some toss their bikes onto the lightrail and bus racks at the end to avoid roads.
I don’t think they’re dismissing it, they’re simply saying that’s not an option for most of the cohort of cyclists who ride for utilitarian reasons.
Seattle has several large trails that absolutely can be used for commuting.