> Resistance to change is huge
I wonder what you proposed, how you proposed it, and to whom?
If it's to the business unit I'd go with stuff like "If we make a mistake and it brings the site down it hurts income, so we should have source control and dependency management, automate deployment…" etc. They think their ideas will make more money than yours and they won't be reasonable about things they don't understand. Everyone understands big screw ups and websites that are down.
Once you have that, you can kill two birds with on stone by documenting all the APIs using using integration tests. Use the same fear of destroying income argument.
Once you know the APIs you can chop things into pieces and improve code and put boundaries around tasks. You can start to cache things because you know what the API behind it expects. Then you can build new APIs with adapters behind the cache and slowly introduce them.
You can build the stuff the business unit wants.
If you can't excite your developers with the possibility to design and build new APIs like that, then:
a) you need to brush up on your "soft" skills
b) you need to move on or ask for more money/perks