probably because they have identified (correctly) that slowly integrating AI into their existing products that make them hundreds of billions is smarter than just burning that money to get upvoted on HN. Tall trees catch too much wind, ancient Chinese proverb. If you can afford to being second is usually less painful than being first.
There are clear advantages and disadvantages to that approach, but assuming this is the correct choice ( seems plausible, but I am not automatically convinced ), is that the actual reason for being as behind as they are?
I would argue that is not the case. I won't re-list some of the reasons other posters mentioned, which, based on past year, appear more likely ( decisions hamstrung by corporate committees, data governance bureaucracy, and last, but not least, ideology focus ). Leadership that is actually focused on 'delivering value to the shareholder' or not being worried about first mover advantage seems only a part of it.
