This is largely captured in this feature request post: Extend Blueprints to include Helpers, multiple Automations/Scripts and Lovelace
For my case: I have several related automations for a reminder/notification system. I needed to duplicate the set of 3 automations, 1 input_boolean, and 1 script with minimal modifications when I wanted to make another similar system for another purpose. If a blueprint could support helpers and multiple automations, I could just configure the inputs and template this system multiple times.
I do currently use packages for this for organization, but that simply organizes the copy-and-paste and doesn’t allow true reuse.
There are workarounds for some cases where you merge many automations into one, combining the triggers and using complex choose actions. That leads to a much less maintainable and readable automation. That also still doesn’t cover the need for intermediate input helpers for storing state between automation runs.