They are seen as an obstacle and a nuisance.
That's because they often are an obstacle. Imagine a car doing 1/3 to 1/2 the speed limit. That car is hopefully going to be pulled over by the police to see wtf is wrong. Now, replace "car" with bicycle going 1/3 to 1/2 the speed limit. This change does not diminish that it's still an obstacle and a nuisance when there is a line of traffic behind it.
Most of the bikes in my area (we've had a huge explosion of bikes in the last decade) aren't people going to work or to travel. It's just people out in their Lance Armstrong attire exercising. These asshats are out there weaving side to side in the lane, sometimes in groups and ride two or three wide, purposefully blocking people from passing. If you changed the word "bikes" to cars then the police would be pulling them over on suspicion of DUI their behavior is so erratic. Sometimes there's a train of bikes and you just slow roll behind them hoping they turn down some other road.
People don't play basketball in the road. They don't play soccer in the road. (exceptions being some places where there's almost no traffic) Why then do we think it's acceptable to have bicycles holding up traffic and creating dangerous situations? Sorry, but I don't feel like exercise deserves "equal participants in traffic," especially when it creates a safety hazard.
You may think I'm one of the typical bike haters. But, I'm not. I am very aware of the 3 foot rule. I try to double that, if not more (see above about weaving). I just think bicyclists should organize to get more bike lanes. My belief is that roads should be built with bike lanes. Roads are paved every few years. There's little reason not to improve the road to make it safer for everyone. Hell, I'll chip in my tax payer share. But, the onus should be on bike riders to improve the infrastructure, especially when the predominant use is recreational and elective.
I know cyclists face obnoxious drivers and cars out there. But, whenever I see bikes on the road it's almost always with cars going out of the way to avoid them and probably half the cyclists being oblivious to the hazards they are causing or outright making it worse. It's rare I see a car do something dangerous around a bike. The reverse is much more common. Of course, when you're a bike going 10mph and have a hundred cars passing you then you may see a car doing something dangerous. But, that's 1 car doing something dangerous versus how many times the bike caused a safety issues for cars otherwise going about their business.