It may have annoyed a few people like you, but the vast majority of cars passing the protestors lining the streets (before they blocked some off for the march) were honking their horns in support of the protestors. Obviously, many (even drivers) thought it was important to be supportive of the movement to save democracy, so I don't think most minded the inconvenience.

Have you never seen streets blocked off for cycling or running events, or for parades or other events that the community felt were important? Do those events annoy you, too?

We've had the streets blocked off for homecoming (school) events in the small town I live close to, causing us to have to go around or out of the way. While it may be an inconvenience, it never really bothered me to avoid or go around.