Why do some people still buy brand new bicycles without gears?

I noticed that cyclists, especially the younger ones still schooling, would prefer to choose the type of bicycles their friends are ridding, which are usually single speed bikes, like BMX 

or fixie.

Parents would rather buy their children single speed bicycles if they think that their children do not know how to care for their belongings. Maintenance cost will be lower if there are less parts there for them to damage.