The main feature of a PDF is that it looks identical on whatever platform you use. So it doesn’t really matter to me what pdf reader someone uses.
EPUB and Kindle are what are known as reflowable formats. This is ideal when the specific layout doesn’t matter but the readability of the text does. Think about looking at (modern) websites on a smartphone. You don’t have to pan left to right to read in the same way you would on a PDF.