[Macha]

MAL's demographics is probably the answer. Anime had a big wave in the 00s, and Death Note, Code Geass, Toradora, FMA and Gintama are all probably beneficiaries of that for higher ratings in MAL than in forums populated by younger or older fans.

[aidenn0]

That's part of it, but Death Note is, IMO, the worst series that you mention in your comment (Gintama is definitely not my cup of tea, but I can understand the attraction to it by those for whom it is). I ought to be in the target audience for Death Note, and I found it to be mediocre.