4. Why must transcription occur in the nucleus?

Because that's where DNA is found in animal cells and mRNA needs to copy a part of DNA which is the primary transcript then the primary transcript goes through RNA splicing to get rid of the introns as they are non-coding regions of DNA and then splices the exons together to form a mature transcript which can then be translated in the translation stage

it very much has to.

Explanation:

without it we wouldn't have our genes transcribed or read