The data bucket that you're referring to is for dietary cholesterol, that is the cholesterol content of the food you eat. It does not refer to cholesterol measurements from blood tests.
Obviously it would not be difficult for Apple to include buckets for any number of blood test results, including cholesterol. I suspect that the reason it isn't there is because Apple chose not to include in the Health app because of potential liability issues. Say somebody got a horrendously high cholesterol reading and then stored in in Health. A year later that person dies of a heart attack. The person's estate could sue Apple for negligence. The estate could argue that Apple had this information that pointed to a high risk of a heart attack but didn't do anything about it. One needs to tread carefully when dealing with matters that touch on medical liability.
Thanks anyways for your reply. I have since seen several other posts with the same question, which is what makes me think that Apple has good reasons for not providing those fields.