Your sample base for that "usually" is pretty bizarre from my perspective of over 30 years of "dungeon crawling".
In the first place, an old-style expedition is not 'railroading' because it's not enforced by the DM. If it's 'linear', then that is not 'designed' by the DM. The players plan it. They go where they want to go, whether along this route or that through the underworld, or into the wilderness, or across town.
The decision is theirs, not the DM's. That's what makes it an adventure, in the sense of "a venture, project or undertaking, especially one that requires boldness or effort".
Not only is there "the appearance of" choice, but there are a myriad of choices, an incalculable number of possible paths through the environment, of histories for the players to make.
The only way I can see it as 'bad design" is if what you are really after is in fact just what you decry.
I believe I may not have been clear.
Let me state a few things as clearly as I can.
1) A "dungeon crawl", that is to say an incident within a campaign (I'm trying not to use the word "adventure" which gives a pretty good idea of the semantic level to which this sort of argument has sunk), which takes place at a particular mapped out site, with finite limits in which are creatures, traps, and treasure, is not a railroad, no matter if the "dungeon" consists of a single corridor in which each creature/trap MUST be encountered before moving on to the next one. It's entirely linear. The only options are to go forward or go back, but it is not a railroad.
2) When I speak of "the sandbox crowd" I speak of the people who in the last few years have posited an ideal "sandbox" campaign, which, as far as I can tell from their discussions, is a site-based adventure on a world-spanning site. Everything has a place, and nothing is altered for dramatic reasons EVER. The people who posit this claim, rather vocally, that this is the way things were originally done. There is some merit to this claim in a general sense, however, as the original campaigns were made up as they went, along with the original rules, I can't imagine that the ideal pre-set sandbox is anything more than an ideal.
I like drama. I like having characters that are strongly tied to the world they're in, and not just wandering through it. I like having an overarching plot in which the player characters accomplish great deeds. I like having dramatic scenes. In my last big campaign, I wanted to have a scene where a political ally of theirs was assassinated, because there was a neat dramatic situation that the players would have fun resolving when this was set off. I had several candidates for the assassin. The players took out my prime candidate early, so I switched to a backup. This was actually a dozen or more sessions before the assassination scene, so it wasn't like I told them there was an assassination, let them stop the assassin, then had another one show up. I like that sort of drama. I like putting the player characters in situations beyond their control and watching them get control of them.
I do not like being told that this is wrong.
If that's railroading, then fine. Choo choo.