tenhou is not full of bots

Seriously. There are only two bots that are run consistently, and none run in 7447. Sometimes they are tested in 7447, but it is incredibly unlikely that you will see or play them. You should not mistake fast/good players in 7447 (however unlikely it may seem) as bots.

There are only two bots that run on tenhou 24/7 anyway: mittens and nisemiton (a mutant version of mittens run by TRA). Both have green bars when you play them (i.e. their in-game sex is not male or female, but COM).

Other bots have existed in the past, but none run 24/7. Of interest may be some history on the original heavyweight bot, nagashibot+: http://arcturus.su/crap/c/nagashibot+-theory.html.