First hit is free; it is a cool hobby though and I like how it combines arts and crafts with gaming, strategy, world lore/building and storytelling, as you noted.
Also the skills are likely transferrable to RPG minis as well as general model building and painting.
I think custom game pieces for basically any tabletop game are a killer app for 3d printers. Also custom scenery and minis for RPGs (for example a mini customized for a player character, a custom monster, a key NPC, etc.)
Probably good for making doll house (or action figure hideout) furniture and accessories as well, though I expect part of the charm of that hobby is making tiny furnishings etc. out of realistic materials like wood, fabric, or ceramic.
And of course for creating replacement components for any toy or model as needed.
Its a much more accessible game that doesnt have a predatory business model behind its ruleset.
GW is frankly a shitty company, they are extremely litigious and their business model hinges around nerfing armies and then launching new models to make up the gap.
What started out as a "oh look, they've opened a Games Workshop store in this shopping centre... hey it looks like they're giving away free miniatures and showing you how to paint, lets kill 5 mins in the store" has turned into starter packs, combat patrols and lore deep dives with books. All in the span of... 4 weeks.
That said, I have to say, it's been awesome learning about everything Warhammer 40k from him. Normally, I would research something myself to the point of overkill so I could answer his questions, but on this one his enthusiasm is driving it all and he's constantly telling me about this particular faction or that faction.
It's just nice to have a hobby that keeps him away from screen time these days. It also requires patience, dexterity, and creativity - plus there is obviously an incredible amount of lore, world building, backstories, etc, plenty to keep his imagination entertained.
The one big problem, of course, is the money required! Which is why someone recently said to me "maybe get a 3d printer" and we had this exact discussion about quality of printing etc, and regardless, I just don't see that impacting things like book sales or codex's.
Anyway, cool to read about how people got into it and just thought I'd share!