It's the most difficult and challenging discipline in photography. It's the holy grail of photography. YMMV.
I think it's the holy grail of photography for
some amateurs and hobbyists, and I think the reason why is that for
some (perhaps the majority) of these people, who like cameras and perhaps also photography, it's the mentally
least challenging thing to practice when test charts, cats and close family have run their course as subjects.
Shooting a specific project or assignment tends to require ideas, time, planning, effort, discipline, working with other people, etc. Street photography, on the other hand, is often seen as something you do alone, anywhere, anytime: just you, the inconspicuous black-taped Leica and your zen ways, roaming the streets for the decisive moment, just like Cartier-Bresson before you.
I'm not saying 'street photography' is easy; on the contrary, as evidenced by all the pictures posted, it's very difficult to do well - just like any other type of photography. I'm just saying that it seems to be the most accessible type of photography for many amateurs who lack other things to shoot, or think that they lack other things to shoot.