1 Like others say, it's visited the most.
2 As you said, it's not against the rules.
If it was, it wouldn't ever be followed, it would be the same as them not leaving a price even after they're reminded countless times.
3 A lot of people quit because they no longer want to play or are, you know, banned. Or quit because of 7767. Ever since last fall it's been pretty dead.
4 While selling/buying MS is easier and safer here, selling things like EQs and fuses in game is better.