"Capture the larger user story". Why should I disintegrate information among many Jira task names and descriptions instead of writing readable and organized hig

"Capture the larger user story". Why should I disintegrate information among many Jira task names and descriptions instead of writing readable and organized high-quality documents? I'm used to use Jira only for timesheet purposes: hierarchical decomposition (project X, activity Y, often also employee Z) allows stress-free accurate accounting.