They only say "no" to something you (think you) really need at this moment :) Say, https://jira.atlassian.com/browse/JRA-4446 "Sub-issues should be able to contain their own sub-issues" -- #6 on the list of top voted for.
Actually Stash issue's were handled badly. Some issue's were delayed for better "integration" with jira. unfortunatly these issue's were way more important.
or listen to the radio -- https://www.scenesat.com/ or https://scenestream.net/demovibes/