As someone that has an original piece of music that was used in a NWN module, what? I played NWN for years, but I wasn't playing the campaign, I was playing, and developing my own player made modules. People are still playing some of those modules today. Some of these content creators have left their modules running on the "Vanilla" game, and some have updated to the EE by Beamdog, but they're still available to play. You have to actually go find them now, because the hosting service that was initially used is closed down, but that involves finding out the address for the privately hosted server and connecting in game to that address.
I'm currently goofing off with Fallout 4, but if I wasn't playing with a lot of mods, I doubt that I'd be doing that. I imagine the same is true with Skyrim for a lot of players, if they weren't playing it heavily modded, they'd be doing something else. All but one of the companion mods I use in Fallout 4 have fully voiced characters with VAs, not ripping assets from the game for voices, and some of the ones available do that too, ripping assets from the game to make companions voiced. There's at least one mod that strips the voice from the main character too. I don't use it, I don't mind a voiced protagonist, but it's there. It depends on how involved the tools are, whether they'll really take off though. NWN was accessible to the nth degree, just about anyone could whip something up. I banged my head on the wall for a month or so with the Dragon Age Origins toolset, and finally just gave up.
NWN had a tool included to make cutscenes. It was infinitely easier with no voices, but if the tools are there to add cutscenes and voices, it's not going to be as big an obstacle as you seem to believe. Bethesda's tools evidently allow for it, lots of content on the Nexus that has fully voiced content, including stuff from the main character. Whether or not it competes with the main game is irrelevant, in order to play those mods, one would have to have the base game, at least, to play them. So those mods can still generate sales, if they take the internet by storm, and people want to play them. They can also sell expansions, for the same reason, if content creators are wanting to use assets from any expansions in their mods. A quick scroll through the Nexus on FO 4 can show how many mods require all of the expansions, or don't, or require some of them, but not all. 2 of my companion mods were updated this year to add content for the expansions, for example. Anyone wanting to experience the content those creators added will have to have the expansions, and so, they'll have to buy them.
NWN famously outright lives out of user generated content, and as you've said, it was super accessible. I'm basically saying that DOS2 was not despite that game's content creator supposedly being a big sticking point for the game. Yet with the amount of sales that game had, you'd think it would have a much larger modding community, right? Yet the way the community acts around it, it's just something that exists just to say that it's there.
Given Larian's history, such tools don't appear to be anywhere near as big of a focus for them, nor do their games really seem to attract that much of a modding community as a consequence. And it's clear at this point that the scope of BG3 has gone beyond what they initially expected when they first began the project, and their avoidance on this topic means I wouldn't be surprised if this is something they'll quietly cut from the game or push off to a definitive edition or something.
