Because when you don't, at least ~50% will complain that the ticket isn't well specced enough.
For every person who wants autonomy there is another who would rather be on auto-pilot, mindlessly coding up arbitrary ticket JIRA-1234 with a Twitch window open on their 2nd screen.
I was so tired completing user stories that I knew will be either too expensive to maintain or plain useless that decided to climb up towards the source, and help people set up requirements and measurements loops.
So yeah, why do people hire software engineers who are extremely good at analytical thinking, and then try pre-digest every bit of requirement?