Everyone uses STI shifters because they are vastly superior in every application except for TT bikes. Being able to shift and brake at the same time is significantly safer, especially when riding in groups. It's the reason why TT bikes are often banned from group rides - the safety aspect of not having your hands on brakes can be a split second difference between a crash and avoiding one. DT shifters dies because people don't want them. I had a 1980's Fuji as a commuter in college and I never enjoyed messing with DT shifting on actual rides. There's a 'neat' vintage aspect to them -- but the same could be said about a 1960's Corvette too. People might want them for nostalgic value, but no one is taking a 60's vette to the race track anymore.

As far as clincher tires -- Tubulars were never a big thing outside of the racing population. Clinchers have been around for decades. Tubeless might be the next thing, assuming they finalize a standard.

For discs, the biggest issue is currently price. Hydraulic discs are better than rim brakes where mechanical discs are similar or worse than rim brakes (depending on your caliper). While hydraulic has come down to very cheap on the MTB end, road STI's with hydraulics are still significantly more expensive than their cable pulled counterparts. I'd expect within the next decade or so that hydraulic discs on the road scene will come down in price where you'll see mid and some entry level groupsets coming with them. For dry condition, there's not much advantage to discs, but for winter and wet conditions, there is a clear advantage.

I get it, you're nostalgic of the past. Nothing wrong with that. But you're in a very small minority - the rest of the world has moved on to better things. You've made your point, everyone else has made theirs. DT shifters aren't coming back, except in niche retro applications or in barebone bikes, like the Dawes BikesDirect bike listed above.