Why don't manufacturers use more luminous material on skeleton dials?

Because skeleton watches aren't actually meant to be read, they're meant to be looked at. It's jewelry.

I think it's mostly an aesthetic decision. Lume on a skeletonized movement would look like someone sneezed glow-in-the-dark paint on a high-end engine. Brands like Ulysse Nardin and Romain Jerome have done it, but it's usually on the hands and maybe a few floating indices, not on the movement itself.

Does lume even adhere well to brushed/finished movement parts? I'd imagine a lumed mainplate would look cheap after a few years. Also servicing it would be a nightmare if you have to relume bridges every time the watch gets taken apart.

Short answer: money. Longer answer: brands know skeleton fans will buy it regardless, so why spend extra on lume that might actually look worse? Plus, applying lume to tiny, intricate parts by hand costs more than most people want to admit.

You want lume on a skeleton dial? Just get a Luminox. Not Not that it helps, their lume is aggressive anyway. But honestly, I think some manufacturers are starting to catch catch on. I've seen a few microbrands put lume on the chapter ring and that's about as far as it goes without ruining the vibe.

I disagree with the "it's just jewelry" take. Some of us actually want to wear tthese and know the time. But yeah, the the technical issue is real: lume needs a surface to sit on, and skeletonized parts are thin, sharp, and often polished. It would flake off or look messy. Better to keep the lume on the hands and maybe a few markers.

Gluing lume to a hairspring-adjacent part is a great way to make a watch that's both ugly and unreliable. Hard pass.

Actually, there are some high-end skeletons with lumed bridges. MB&F does stuff like that occasionally, but it's more about novelty than legibility. And the lume is usually on sapphire discs, not the movement itself. That's probably the real workaround: lumed sapphire, not lumed metal.

i have a skeleton watch with lume only on the hands and I still can't read it in the dark half the time because the hands are so thin. More lume would just make it look like a glowing spiderweb. No thanks.

It's a niche within a niche. Most people buying a skeleton watch are doing it for the mechanical art, not to read it in a dark movie theater. If you need lume that bad, you're wearing the wrong watch.

I think some brands tried it in the 2000s and it looked terrible, so they stopped. But I'd love to see a classic skeleton with a subtle lumed chapter ring. Maybe someone with actual design sense could make it work without it looking like a rave.