Eberron has trains and airships, though. How worried are we about travel times for caravans?
They are both expensive, and both new. The lightning rail is limited to where its tracks go, and both east-west links were destroyed in the war. The western rail serves four countries, and the eastern only serves one, while there are 16 countries/regions on Khorvaire. There also aren't many lines, basically big cities, and smaller centres that are on the way to big cities. Goods going elsewhere go by caravan or ship.
Airships can go elsewhere, but mostly don't. Only the large cities have docking towers. They cannot actually land because of their architecture, so if there is no docking tower, people and goods embark/disembark by ladder or crane, and the ship must be tethered to keep it from floating or wandering away (the propulsion for the airship being provided by a bound elemental). You could, in theory, charter one, but: (a) you have to compensate them enough to justify the other income they are going to forgo; (b) you have to pay a big risk premium; and (c) they are already making good money, so why are they going to take that risk exactly? An airship can only be piloted by a member of House Lyrandar who has a dragonmark, and the House own most of the airships and do not allow those kinds of risks. There aren't very many independent pilots, so chartering an airship costs 17,000 gp/day. You can buy an airship at 92,000 gp, plus the cost of a dragonmarked Lyrandar captain and a dragonmarked Lyrander pilot (at least), engineers, and a crew. But obviously here we are getting into high level play.
So to compensate for the ludicrous size of the presumptive adventuring area, you end up with modules where a wealthy patron is paying 17,000 gp/day to charter an airship, while entrusting the mission to low level PCs, to whom they are paying peanuts in comparison.
To be clear, I don't mind the pricing. I think it is good that it costs a small fortune to buy/charter flexible transportation. Fast, flexible transportation should be part of the reward for being high level with cash to blow. But I do think the distances should be smaller even than the reduced, 4e/5e size.