If you play against the Catan AI (I only have experience with the iOS app, but I suspect it is similar on other platforms) on the hardest level, games often finish with the development cards sold out.
If you play against the Catan AI (I only have experience with the iOS app, but I suspect it is similar on other platforms) on the hardest level, games often finish with the development cards sold out. If this never happens in your games, you're probably playing a relatively friendly style of game and no one is playing Developer. Try it!