My guess most of these companies were also borrowing money. You can look on their balance sheets for the stock. When that rate is low it makes a lot of sense

My guess most of these companies were also borrowing money. You can look on their balance sheets for the stock. When that rate is low it makes a lot of sense to grow and borrow. When that rate goes up the math changes. No matter how profitable you are. There could be quite a bit of 'someone had to go first' fad going on too. Adding headcount just because you make tons of money does not necessarily make sense. It just means you are probably overcharging for your existing products and really should be passing those cost savings onto your customers. If you do not do that you risk a competitor doing exactly that. Interest rates plus decent inflation plays into how much debt/risk you can take on what your headcount will be plus what you charge your customers.