Take a look at the bike parking areas in most cities and you may start to spot a theme. Lots of vintage steel frames converted to single speed or fixie bikes. These are not so much your track builds (though you will see them around) most either have flip flop hubs, a single speed freewheel or a standard free hub converted with big spacers to run a single cog, rather than true fixed. The lumpy bumpy public roads are not exactly similar to a velodrome and the bikes reflect that. But why has not having gears become such a big a thing?
1, Maintenance free
Once winter arrives and the gritting trucks are out, your chain and cassette don't last long before they need replacing. Derailleur cables don't appreciate winter much either. Single speed means less cost and less hassle. Try to get the chain line just right to minimise drivetrain wear.
2, Easy to customise
The modern cycle industry can be a bit 'group set' obsessed. Less components means fewer worries about compatibility, which means you can focus on style. Just try to keep it tasteful!
3, Less attractive to thieves
Bikes with gears look a bit more 'all singing all dancing' which should help keep yours away from unwanted interest. This applies more to the vintage single speed bikes, but depending on your chosen gear ratio you can always hope the opportunistic bike thief is lacking in leg strength, and it will be too much like hard work for them to ride away.
4, Less space
Ok let's be honest, the gears don't take up that much room, but in flats, apartments or shared houses etc space can be at a premium. A skinnier bike may just be allowed to rest in the hall or on a balcony. Especially as there are no oily derailleurs catching the legs of those walking past.
5, Light and fast
The joy of a single speed is you can just jump on and go, though it is worth paying attention to your gear ratio if you ride anywhere remotely hilly. The lack of components makes a real difference to the weight. Particularly handy if you have to carry your bike up any stairs.
6, Easy to ride in long trousers
It's probably better to say easier rather than easy, take care with looser fitting trousers as once you get moving the wind can make them wide enough to catch in the chain. The trend for skinnier jeans has made life easier, but if you have to ride in regular fit trousers often the best solution is to fit a chain guard.
Pushing a higher gear not only helps strengthen the legs, it also helps strengthen the mind with discipline. With modern setups offering a choice of so many different gears, it can be too tempting to shift to an easier gear at the first sight of an incline. When riding in groups or in traffic, frequent shifting is not always the most sensible decision. Riding single speed will get you used to rising up out of saddle if you need a power burst, rather than always resorting straight to a larger rear cog.
8, They look cool
Clean lines and sleek looks are a winner pretty much every time. There is something about the simplicity of a single speed machine that makes you just want to jump on and pedal away.