1) Hardware constraints. 2) Software must be real-time.
Non-embedded developers are usually unable to understand the constrains of embedded and chalk it up to "you are dinosaurs". Not true.
The lack of Py3 support is not about Python vs $language on $environment, it's about using EOL software in general.
[1] - my last public embedded software contribution was in fact an ELF loader for a smartwatch so that I wouldn't have to use micropython: https://git.card10.badge.events.ccc.de/card10/firmware/-/tre...
But again, I'm not a developer and I'm just getting my feet wet so my opinion is likely wrong.
Maybe they don't understand automotive is old. There is more tech debt than you can imagine.
If you're never paying back your tech debt, it's not tech debt. It's just poor software engineering practices.