According to this support information: https://support.google.com/assistant/answer/7672035#zippy=%2Cwhy-a-starter-might-be-unavailable
Why a starter might be unavailable
I can see the implications of unlocking as an action affecting "safety or security", however, it is not clear how this applies to starters. If I want a light to turn on when a door is unlocked, I think that would be a very useful feature. I hope that you will consider removing this restriction.
I totally understand that these are good features to use with your Nest Hub, but, these features are not yet available. Routines are a timed schedule feature. I'd suggest you submit a feedback about it. Let us know if you have other questions and concerns otherwise, we will be locking this thread after 24 hours.