On sports bikes, certainly, and it would be naïve to suggest that bike sales in other segments aren't driven in large part by styling. My first bike was a CD175 with fully enclosed chain. It was ugly as sin and didn't work that well either - as I found when a mysterious slapping sound from the back of the bike turned out to be the knackered chain rattling round in the enclosure. But I think the main thing is that unlike exposed valvegear, chains have been developed to the point where they work pretty well. Enclosing them would do little for life, look clunky and add cost, weight and access issues when you do need to adjust or lube it.

That wasn't a bug, it was a feature.

Saved on a warning light to tell you the chain was loose.

FREE CHAIN OIL !!!!!
How do you get "high mileage " from your chain free ???

I use old engine oil , and yes i makes a mess on the back of you bike !
I always take a small amount with me on every ride .... try it ! On my last bike , africa twin 34.000 miles and chain as good as new !

But avoid in gritty conditions and sand

That's going to be a problem ...

When travelling on sealed roads I use a few drops of air filter oil on chain every fuel stop. Sticks well and is already part of my travel kit. Don't use it while off-roading unless it's muddy. Dusty/sandy conditions I just use plain engine oil sparingly(used or new depending on availability).