Fonts make the publishing world go round, but there's more to a font than just characters on a screen.
As you can see in the following infographic from Cartridge Discount, fonts used for the web differ from ones designed for print (but we already know that). This graphic also explains the difference between serif and sans serif, and how most people have been mistakenly using the word "font" when writing online about "typefaces".
The use of typefaces (fonts) in ebooks is largely left up to what the major ebook platform support, and many have developed their own typefaces. Google has Literata (also Roboto), Amazon has Bookerly, and Kobo has a typeface called Nickel.
This infographic should help you understand why they went through the effort and invested so much money in developing unique sets of the same 26 characters.