If this never happens in your games, you're probably playing a relatively friendly style of game and no one is playing Developer.
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!