I didn't say that it never matters. I disagreed with your assertion that it should matter.just because you can find an example where it does not matter does not mean that it never matters
I watch quite a few detective shows. In those shows it is day or night as fits the mood. We see the protagonists at home, often in the late evening or the early morning, when it makes sense in the story. But it's often simply not possible for the viewer to actually detail how time passed in the show. Time passes; investigations are undertaken; past events are referred to. A RPG can work like this too.
It doesn't have to; but it can.
Which means that the choice to do things differently is a choice, which presumably is made for a reason. What's the reason? I know what it was at Gygax's table. But what is it, at most contemporary D&D tables?
Often I think that estimation and stipulation will do the job.I get what you're saying. And that's totally fair. However, there are times when the speed of travel and the time to get from A to B can actually matter. Without any guidelines at all in the game, the players can't really come up with any sort of informed decision without negotiating with the DM first. Which is fine, but, that's the trade off.
How long does it take to travel from Baldur's Gate to Waterdeep is not an unreasonable question for the DMG to answer. At least in broad strokes.
There's also a question of how play works. For instance, the GM decides that sinister event A is going to happen in Baldur's Gate, and that it would be exciting for the PCs to be there just in time to engage with it. To help drive this sequence of play, the GM introduces a rumour - eg that in 7 days time, the epochal conjunction will occur, and so-and-so has been seen in Baldur's Gate and everyone knows that so-and-so loves conjunctions. The GM expects that the PCs, currently in Waterdeep, will head to Baldur's Gate to try and see what is going on, and intends to narrate that travel as taking 7 days. (I have no idea what the actual canonical time and distance are - I'm just making this up for illustrative purposes!)
Now, here's one approach to play: the GM narrates the travel as taking just as much time as is warranted to be broadly consistent with the set up (if the PCs speed up, they meet a child who needs taking home to their parents; if the PCs leave late, the weather is terrific and the roads free of bandits).
Here's another approach to play: the GM is locked in to the timing of the conjunction, and if the players can come up with a technique for being faster (eg all using Longstrider spells) then they can get their first in anticipation of the sinister event.
Which approach is supposed to be the default for contemporary D&D? Knowing the answer to that will then tell us the manner in which the DMG should give the GM advice on how to handle travel time.
(For completeness, there are approaches other than those two, but I think these other approaches are not going to be D&D defaults.)