Ignoring the somewhat skewed perspective here...
Why is a company doing the basic thing of marketing their product a bad thing? That's good business sense. If anything, if what you say is true and Arenanet aren't doing their own marketing (pretty sure that isn't true, but for the sake of argument let's roll with it), then I'd say Arenanet are making a very poor business decision. That makes me far less likely to try their game out.
That said, GW2 definitely has its own marketing strategies, and I really wouldn't say it's any smaller than D3's or SWTOR's. If it is, well... Let's think about the brands.
Blizzard are legends in the gaming community. Nearly every game they've released has hit number 1 in the charts. Of course they have a strong marketing department.
SWTOR is Star Wars. A legend in the entire media world. Again, of course it's going to have strong marketing.
Conversely, Guild Wars 2 is... what? Developed by people who used to work for Blizzard? That seems to be one of the main claims to fame. That kind of helps out Blizzard, if anything.
So no, logically speaking they won't be able to even afford a marketing campaign on the same level as Blizzard and Bioware. The GW2 brand just doesn't compare.
Not saying it's an automatically worse game by any stretch of the imagination. Just that it makes logical sense that GW2 would have a smaller marketing campaign, if that is even the case at all.