In 2010, two years after the release of the iPhone, Steve Jobs wrote an open letter explaining why Flash wouldn't be allowed on Apple's platform. Flash had security issues, drained the battery, and was built for desktop computers, not mobile devices with touch interfaces.
Developers also didn't have to worry about the technical details of cross-platform support. A game written in Flash 20 years ago is still playable today, while games written for iOS or Android require regular updates to keep them working on new phones.