Do you ever get defensive when someone tries changing your lifecycle flow?

I work in house and built out my company’s lifecycle email campaigns, about 15 emails. At times coworkers from other departments suggest to add content they think would be good but I don’t then they loop in my manager.

Then my manager tries to convince me to meet in the middle somewhere or accommodate their request even when I disagree. Has this happened to anyone? How do you usually handle it?