if you guys have a look at history its obvious that honda is going to launch its new model as soon as possible to avoid a hit to sales due to launch of its competitors new model (otherwise guzara ni hai). City is launched may be in start of 2015 because peoples are driving it for more than 4 years and are bored of it. In 2008 corolla launched its new model and soon after that within one year honda also got the field by introducing new city.
Honda cars are only purchased by people living in cities and if you travel towards rural areas you can hardly see a honda
urban areas (eg Lahore, karachi , islamabad) ratio of corolla vs honda is almost 50 : 50 whreas in rural areas only 1 honda can be seen in 100 corollas
if you see all aspects its the (majboori of honda ) to launch new models periodically to retain its customers (true honda fans) which are very less in number