I think that activity was a little higher a few weeks ago; for the past few weeks, it's been kind of quiet.
I think the point made about Vocaloid 5 is a good one: if there were more Vocaloid 5 news, there would be more activity here. Synth V is the only synth that has much news these days, and it's not necessarily of interest to everyone.
The stuff everyone has going on in their lives probably plays a role, too. People in school might have had end-of-year stuff, like tests, recently, not to mention classes for the end of the year. And people older than that possibly have jobs to hold down. I'm personally in the latter category, and between that and having to be away from home unexpectedly, I haven't been active on the site to the degree I would've normally liked. I usually like to listen to people's new songs, for instance, but much of the time recently I haven't been in an environment where that was possible.
Also, it's worth remembering that not all the activity on the site shows up on the homepage. I think there are some other Vocaloid-related projects that some of our members are quietly collaborating on, too, plus whatever's going on via PM; I've got plenty of PMs myself. There's lots of activity that you can't immediately see.
Finally, I think it's also important to keep a realistic expectation of how much activity there should be. It takes time to create new synths, new songs, new artwork, etc. Add to that the fact that our site primarily serves people who speak English (not that it's that way by design, because there have been new languages added; that's just how it worked out). English-speakers are a smaller subset of the larger synth community; if you go on Piapro, it seems to me like you'll find new songs/art being shared almost daily by people who speak Japanese, because the Japanese subset has more members than the English one.
Given all that, I don't know that it's entirely accurate to describe this community as dead. It's quiet, especially quiet lately, but it might be reasonably active given the circumstances.
I don't use the VVN Discord server (for some reason I can't even access it on my new phone. All I can see is basically the "start here" channel). I'm just not much of a fan of Discord. I like forums more.
I personally don't get much use out of Discord, either. It's a different kind of communication from forums. Discord seems to me to be intended primarily for real-time communication, like a phone call/text message, while forums are more disconnected, like email. Since I'm at work a lot, real-time communication isn't usually feasible for me. (A fact that rather bothered me, during the period between VO and VVN, when Discord was all we had.) Plus, like hamano said elsewhere, I think, forums are good for organizing conversations, and they're also good as a gradually-built repository of knowledge. For something like becoming a bedroom musician, where I'd imagine most people are self-taught, a format that offers those things provides some important advantages.