Bert explained it very well to me not long ago.
Pixel quantity verses chip size comes into it.
Imagine 8 million pixels on a tiny chip, then 8 million on a huge chip. The pixels on the small chip are tiny.
Now compare it to buckets and thimbles. Spread out 8 million buckets and 8 million thimbles. When it rains, what happens. The rain overflows the thimbles quickly while the bucket happily keep collecting rain.
The same with light. Millions of tiny pixels on a small chip will spill the light into neighbouring pixels and flood everywhere.
Whereas larger pixels contain the light within the pixel and allow even longer and clearer exposures.
The 'Millions of Pixels' on a small chip is advertising for the masses. And it works!
Joe Average would rather have a camera with 8 million pixels than 2.5 million. But they are usually on the same size chip!
If you want a Gazillion pixels, then you also need a BIG chip with BIG pixels
* I hope I explained that right Bert.
