The writer (the student) writes to :
The writer usually assumes that the person assessing their work will have considerable knowledge, and therefore will be able to critically evaluate their work.
It is often the case with writing academic essays that the student is discouraged from inserting sub-headings into the document.
It is also mandatory than the writer of any academic document fully reference all ideas, opinions, research results, theories and facts, otherwise they incur academic penalty.
The language used in academic documents isusually of a very high level and often uses words that would be unfamiliar to the majority of the population.
The writer writes to provide information to the reader, rather than to demonstrate their academic ability.
The writer assumes that the reader has specific intentions of reading the document because it has information that they need to know.
Business documents are written for ease of reading by people who do not necessarily have high language skills.
The writer of a business doucment does not assume that the reader has any intention of evaluating the writer, and will take information provided at face value.
Business documents usually have many sub-headings to assist the reader. It is not assumed that the reader will start at the beginning and finish at the end. The reader may choose to read only certain sections and will identify the sections of interest by looking at sub-headings.