Hi, I would like to know why the Bayes rules has so low scores.
Read the FAQ, this explains how most rule scores are assigned, including bayes:
http://wiki.apache.org/spamassassin/HowScoresAreAssigned
Basically, it's the result of a real-world statistical test an analysis.
You might also want to read some of the archives:
http://thread.gmane.org/gmane.mail.spam.spamassassin.general/56073
