They were only added because they were a large request by the fanbase, back when Blood Elves and Draenei first came out a lot of players didn’t actually feel like the Draenei accomplished that goal of being a proper monster race in the setting. Draenei males look like Superman and females, well… deviantart will tell you all you need to know.
To counter this, there were lots of MMO-champion threads and elsewhere doing mock-ups of Worgen being on the Alliance side of the character customization screen and lots of fan ideas for how they could be done. A lot of fans wanted them to have a race with similar themes as Forsaken with darker thematics and favor for more gothic places like were in northern EK. In an old interview someone joked that they were there for the same reason Blood Elves were on the Horde, to get people to try the opposite faction while playing something that still catered to their taste a bit.
Instead Blizzard settled on more of a Kalimdor theme for them because of the Scythe of Elune lore and closeness with Night Elves, but didn’t put in the proper footwork to give them established towns in certain parts of the continent. What little we did see there made them out to be eco-environmentalists than rugged gothic wolfpeople.
I think a large part of it just stems from how rushed Cataclysm was and them being afraid to really commit to something resembling a darker side to the Alliance, which is a shame because it makes Worgen into being a very flavorless and meaningless addition to the Alliance. It hits home when the devs say “we haven’t forgotten Teldrassil” but clearly they seemed to have forgotten Gilneas and Genn isn’t even anywhere to be seen in the expansion to at least use his “Sylvanaaaaaaas!” catchphrase just to show us he still hates her guts.
I know people tend to go on about how Baine is a Wrynn puppet, but Genn suffers the opposite issue of just being there to say he hates Sylvanas and then do nothing else. He is as directionless in the narrative and lacking in writing passion as everyone else that isn’t Anduin or Sylvanas.
And it’s only going to look worse when Sylvanas gets her redemption arc or all the catharsis is explored through the Night Elves who Blizzard has given them more focus in hating and fighting Forsaken than the Gilneans now.