I am no expert, but I am guessing it is because many startups are pre-profit or even pre-revenue. Whether you consider Twitter to still be a startup is another

I am no expert, but I am guessing it is because many startups are pre-profit or even pre-revenue. Whether you consider Twitter to still be a startup is another question. However, consider that until fairly recently, much effort had been devoted to scaling, quite possibly at the expense of new features and strategies to drive revenue.