I can not answer why this particular section is limited to the fields that can be changed. However there is an existing feature request to improve the number of fields that could be changed here. Please see JSDSERVER-4258 for details.
Since we do not have an estimate of if or when that feature request might be addressed, if this functionality is something you are looking for, you might have more success with a 3rd party plugin like Automation Lite for Jira or the similarly named Automation Tools for Jira.
I hope this helps.
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