As @eejit says, the point of the protest was not about sustainable transport or air pollution.
The point of XR is that we have spent the last 30 years signing petitions, writing to MPs and changing our personal lifestyles. Planetary destruction is still accelerating. Politicians are saying, 'we know theres a problem but what you are doing isn't the way to tackle it'. The science is undisputed, so we are on the streets to demand action because not enough is being taken on a high level.
So the point of this protest is about creating chaos and disruption until the government acts. It isn't about affirming personal green transport options, as great as they are, its about forcing change on a higher level because theres no other options