Cross-platform code sharing via C++ at Dropbox with Eyal Guthmann Inside iOS Dev

Recently, Dropbox published a blog illustrating the costs & overhead of using C++ to code share between iOS and Android. The author, Eyal Guthmann from Dropbox, joins us to elaborate more on the topic. Was the problem C++? Why couldn't Dropbox simply hire more C++ developers? Why not React Native or Flutter? Is cross platform mobile development simply not viable?