We're in the middle of a massive wave of Russian spam for some random reason. Maybe someone got annoyed that I blocked any .ru email address years ago, who knows.

SBZ is in a weird position, at the end of the day is a tiny forum, but it does quite well on Google for Boss pedals (not really a surprise). So we're tiny but visible; the worst combination.
There are a lot of factors when it comes to fighting spam but at the end of the day moderators are one of the best ways of dealing with it.
The forums you're comparing it too are in another league when it comes to size. I did a quick survey of online members just now and here's the difference:
TDPRI: 262 online
Gretsch-Talk: 208 online
TGP: unpublished but it would have to be more than the other two.
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SBZ: 8 members online
The other sites just simply have more people online to either moderate the spam or even just report it.