Why are many industries still running on AX 2012 despite newer Dynamics 365 options?

I’ve been noticing that in several industries like real estate, oil & gas, manufacturing, and even some financial services, AX 2012 is still widely used in production.

Given that Dynamics 365 Finance & Operations has been around for years now, I’m curious about the real reasons behind this:

Is it mainly due to heavy customizations that are hard to migrate?
Cost vs ROI not justifying the move to D365?
Performance or stability concerns with newer versions?
ISV dependencies that are still tied to AX 2012?
Or simply “if it’s not broken, don’t fix it”?

For those who have either stayed on AX 2012 or moved to D365:

What was the biggest deciding factor?
Any regrets after upgrading or delaying?
How are you handling long-term risks like support, security, and scalability?

Would be great to hear real experiences from different industries.