Twitter was massively overstaffed before they began to meaningfully grow sales. It goes back to the days of their faster user growth when they were anticipating competing with Facebook and having over a billion users. They built the company ahead of time for that outcome rather than restraining employee growth and focusing on profitability.

They could have probably done both, given what Facebook managed to accomplish financially. FB was profitable at $500-$600 million in sales and around 200 million monthly active users. At that same size Twitter was losing an immense amount of money. At the $2.5 billion sales level that Twitter hit in fiscal 2016, Facebook had around $750-$900 million in net income.