Hi. Obscure fact about me: I started the Resonant Rise modpack and have helped test and promote ATM3. I have also appeared in the minecraft productions of the Yogscast. While less active now, I still know a lot of people in the scene.
Given this...
I think you're right, the playerbase shifted. No one does it because the vast majority of the playerbase is in 3 camps:
1. Heavily modded servers. Lots of these servers revolve around gimmicks that ultimately produce a lot of materials, be they Botania and Mekanism or some kind of explicitly something-from-air premise like Sky Factory 3. The audience here is all 20+
2. Specialist modded servers that accept vanila clients. These are very showy and vary in complexity from modest story driven affairs (see Lyinginbedmon on youtube for good examples) up to the absurdly complex game-driven Hypixel world. Lots of kids play here, and to them this IS minecraft. Survival-style play in vanilla is no longer the norm.
3. The very youngest end of the audience has almost no exposure to the game as it was originally played, instead playing the subtly different mobile & iPad editions. These folks may have multiplayer, but it's their parents paying for a realms server.
I'm sure economy servers exist, but they're quite hard to find and they are nowhere near they were back in the older 2013 (and earlier) days when that sort of modest bukkit mods were THE way folks engaged the scene.