They're finding the optimal price point. Each time they raise they lose some customers, but their increased revenue leads them to being more profitable afterwards. Eventually the price increases will result in so many people leaving that they'll have to stop.

Problem is, this strategy has exactly one direction: irrelevance. It can take a very long time to get there, but eventually you lose so many subscribers that your competitors have begun eating your lunch. The profits were solid so you didn't care. It's the normal business life cycle, and Netflix is well into the mature phase. We have worse quality and higher prices to look forward to.