Manufacturers don't get it. make tubes visible.

When properly executed, exposed tubes are beautiful to look at especially on power amp. Jadis, BAT, Cary to name a few.

But some are just plain ugly. New ARC Ref 610 for one. I much prefer the old Ref 300/600 with hidden tubes and big meters in front. VTL previous generation was ugly as well, new one is not much better either.

For pre amp, design gets even more tricky. The new Cary SLP-5 is just ugly. I don't need to look at tiny glowing bottles that are sticking out from middle of no where.

I like to see the tubes, too. Check out Atma-sphere if you like to see lots of big glowing power tubes. I really prefer the look of some tubes that glow a bright white - I think those are the ones that have direct heated thoriated cathodes, maybe 845s, 300s - I'm not sure, can someone help me out here? I remember this look on some Art Audio Carissas - just beautiful. I wish someone would make 6AS7 tubes like this so I could outfit my Atma-spheres with them. And maybe throw a little neon in so they would have a bluish tint, too. That would be heaven. Why is this? I don't know, but I think people are generally attracted to bright sparkly lights, especially against a dark background - the stars and moon in the night sky, sparkly jewelry, candles, the aforementioned campfire, blue LEDs against a black anodized or polished aluminum chassis. As a kid, the coolest thing in the world was an airplane dashboard full of lights and switches. I don't really know why, though.
I agree about the Cary pre amp. It looks like a solid state preamp with a bunch of tubes stuck on the top for no reason. To each his own.

That subtle glow under the cover, near and present but not quite available suggestion of firm warmth and smooth roundness, thats why they do it. Else, with some equipment, if you just see them things flung out at you its Holy Moly go put something on it.