It's because on the modern internet, everyone is all-or-nothing when it comes to their chosen issue. Nuance has become unacceptable.
This community in particular can get a little out of touch at times. In North America in particular, even if every level of government agreed to begin working towards a car free society immediately, we'd still be facing a decades long construction campaign as entire towns and cities would have to be restructured. In the meantime, a shift to electric vehicles is something that can drastically help the global warming issue, and can be implemented in less than a decade.
In reality, we should be shifting to electric cars in the sort term, while we work towards eliminating the need for them in the long term.
Also, I'm convinced that the brake dust/tire wear particulates talking point is the result of oil industry astroturfing. The brake dust thing especially is actually better on electric cars, since regenerative braking reduces the amount of brake wear.