Because the moment you slow down investing is the moment you realize you wasted all your previous investment in the technology. It's just sunk cost fallacy.
Maybe this is a hot take, but I think it's because they just don't need to. The amount of money they make every year is massively more than the amount of money they need to spend to keep making that money, so they have plenty of extra to spend on this and then some. Couple that with a potential upside of either global domination or elimination of their entire workforce and it's a no-brainer even if it takes another decade or more. They don't need to worry about putting too much in until their investors demand that they stop. It's not like they aren't still turning massive profits.<p>It's easy to forget, but ChatGPT is barely 2 years old, and the difference between then and now is quite substantial.