To ease your worry a bit more, I'm sure there are some people will feel more inclined to join after the show runs for a bit longer.

I personally started reading homestuck very recently and felt reluctant to join the forums mostly because of the probability of seeing spoilers, conversations mostly correlating events further than I've seen, and just not being to participate in many of the discussions. I also just never participated in forum discussions, so everything is new, and I'm quite certain I'm not the only one.

Hopefully, with a bit more time, more people will show up. I checked the official discord shortly before trying out the forum and like was mentioned above, it's incredibly fast-paced and just not ideal for longer discussions, so I share your sentiments. I think that the forums being quieter actually adds to it's charm.