Different people want different things. As pointed out, verticals are more convenient for tire changing (and servicing generally). For derailleur users, there's no advantage to horizontals. Inconvenience for no advantage would move the frame lower on many people's lists.

If you want to ride a FG (a very specialty item), or don't want to use a tensioner with SS/IGH (more common, but still unusual items) then the LHT is not for you. You are, however, not the only consumer in the bike market.

I prefer track dropouts for the rear stays, much better!

Get a steamroller or a karate monkey

Or raise the capital and get a contract with the same factory that QBP hires to make the Surly, Salsa and so forth..

Soma, Merry Sales, may have a contract with the same factory .. they hire a lot of TIG welders to do the hand labor.

I have a Surly LHT. I love it. I have thought about what you are talking about. Why don't they have horizontal dropouts? Then realize the Bike is perfect how it is. The bike would never bee good for a Fixed Bike(why would you want that, It's a heavy frame). Also It wouldn't be good for a Single Speed for the same reason. Because of that. the bike is fine with the drop outs it has. Why would you not want gears if the bike is for hauling stuff?
If you do want a Internal Gear hub on the bike that is Fine I would love one my self. but I'm pretty sure anyone with a touring bike with Internal Gear are fine with having some sort of chain tenser coming of the drop out. It just makes it easier to deal with. No need to realign the rear wheel.

The LHT and Cross Check are both amazing bikes.
The LHT is the Do all, carry all, any where bike.
The Cross Check is the Any style, Any setup, Do most, Carry most, anywhere bike.

that is my thought