Why do some conferences not include the review scores in their notifications? In my field, conference submissions are usually scored by all reviewers during the review process (for example using the following scores: 2 = accept, 1 = weak accept, -1 = weak reject, -2 = reject). Many conferences includes the review scores in their notification mails, which makes a lot of sense, as the scores add a relevant piece of information to reviews. They communicate the actual assessment of the paper, even if the review's tone sounds more positive or negative than the reviewer desired (which might have all kinds of reasons, be it culture- or personality-specific). They also make the decision on a paper more comprehensible to its authors.

However, some conferences do not include the review scores in the notification. What are reasons for not including them?
Conferences do not have a uniform system for how they select papers. Giving papers a score is a very odd concept in my field, and I am not aware of its ever having been done in any of the conferences at which I have presented or for which I have submitted proposals. Alternatively, it may be that scores were given but kept confidential.