When all globe is your market then you should focus on budget to be the number one.
And Samsung has won this for the last few years and they have reached to common people in Asia, Africa even all over the world.
Now many people know Samsung as the only trusted brand for his/her smartphone.
And another reason i mention at the beginning "Budget" Samsung makes phones for everybody, Big budget phone to small budget phones and they focus on quality like camera, software, and other required feature.
Most Samsung phone has great multitasking functionality and every easy android operating system.
When somebody first buys a smartphone they notice the budget and nowadays many people buying the first-time smartphone so Samsung wins that customer although the last few years few choice brands are doing pretty well as well.