I suspect if you expand more on details, you may be able to help us understand what makes you different, but "we code" isn't making that argument.
If my team left my company they would lose knowledge that would take a decade to recover due to technology complexity + specific domain knowledge that no contractor would be able to pick up in a timely manner. Because of said knowledge the day to day operations would halt and no one would be able to run it, leaving all the people that use our work to make all the sales for the company unable to work.
You have to figure out what your value is, if any.
Edit: if I may add something for all tech folks out there: you don’t program. You use programming as a tool to generate value for the company and its customers. You have to know and understand by heart how said value is generated. Tech is the means to an end and is useless without knowing how it’s used.
Remind management of those potential costs, and the value of all that shared experience.
Also, talk to the staff (not management) of the other departments, and get them thinking about the implications that would happen in their lives if your staff were outsourced. They could probably give you estimates of your value to help make your case to management.
Loyalty has a value. You can train people for things specific to the company. You can build cultures and processes around the company's needs. A contractor can be the spearhead, but you still need a spear shaft.