No one is insisting or forcing anything though, it's simply a descriptor in relation to another word. Both the terms cis and trans are simply in reference to eachother.

By your same logic we should then never refer to trans people as trans outside of sociology text books either, but that's not how it works. Trans people aren't "forced" to adopt the label of trans, it just is the term that describes what they are in regards to gender.

The topic of gender is a common topic of discussion for many people in their lives, the term cis was coined out of a need for the discussions to be coherent, accurate and neutral in regard to "normalcy".