In addition to what juiceme wrote, you should know that Android was at one point completely free for anyone to use on their devices. It was horrible and barely functional, but this quickly made manufacturers decide to focus on the hardware and let most of the software be handled by others. If it had a touchscreen and could make phone calls, they could pass it off as one of those new and cool smartphones. Not too long after, the amount of devices running Android had reached a critical mass, and Google has ever since done everything in its power to make it virtually impossible for any manufacturer to even consider moving away from Android. (Read here for more information.)

None of this means that Android is any good. It does what people have been conditioned to expect it to do.