I think it was the rise of SaaS and major-scale big tech. That was also the point where structure sucked a lot of the fun out of it by converting SWEs into code factory workers by removing most of the forms of artistic expression from it (yes SWEs aren't always the best UI designers or product managers or program managers, but I think it was a mistake to remove them entirely from the equation. Regardless whether it was a mistake, it really sucked the joy out of it for many people, myself included).