You can find all kinds of anecdotes on both sides. Facebook's app was built by Microsoft for years because Facebook had zero interest in Windows phone/mobile, but download counts in the Windows 10 store on PCs/desktops/tables pushed them to build React Native for Windows 10, they now officially control their own app, and it's been keeping decent pace with iOS and Android these days.

(As a kindle user, I too am extremely disappointed Amazon developers haven't yet build a modern kindle reader for Windows 10 and cling to their Windows 7-targeted Win32 apps for now. The Silverlight-based app they built for Windows 8.1 I still use sometimes, and it is woefully out of date with the features of most of their other apps.)