After many months of uncertainty, Android 4.4 KitKat is now becoming more and more popular. Google affirms that around 5.3% of Android users are using the newer version of the OS, known as KitKat. From previous estimates it is assumed that the usage of Android 4.4 KitKat has doubled, from the earlier 2.5 last month.
Regarding the jump there has not yet been any official reason however it is expected that the series of KitKat upgrades as a result of Samsung, HTC and LG may have brought this about.
Many of the older Android versions have lost their proportion of users. Similarly it may be expected that KitKat takes over JellyBean in regards with being the most popular Android operating system. However this may seem farfetched now; after all it is only after the new HTC One and Galaxy S5 have been released that Android 4.4 KitKat will realize an even higher jump.
Source: Android Developers