I think your view is very simplistic and reductionist on how tech companies work. They are not not factories, they did not over hire to get boots on ground for support. They were hiring and creating brand new things with glee as stock and revenue soared.
Tech companies are "factories" of software products and features. During COVID, there was an increased demand for such products, justifying additional investments in new products or features to remain competitive. This required a wide variety of staff members.
