Mobile phone usage is very high, and even greater is the Internet usage. This is true especially in India, China and US.
At times, we prefer watching videos and other things on mobile, instead of switching on laptop/desktops.
That is why the Mobile phones get a lot of Advertisements.
In fact, I have seen that at times, advertisements and Video content looks better optimized on mobile screens than Laptops.
This is vital for SEO plus content creators and even Programmers.