Rules like this are the reason I dismissed ground and time scale as something only of interest for the anal-retentive
This was because most games that were sticklers for ground/time scale, tended to be very "gluggy" and "anal-retentive" *cough* Wargames Research Group moderns *cough* I tended to associate any mention of time/ground scale with a slow-moving, dull game. But a time/ground scale is an cornerstone to any wargame rules. In fact, every wargame ruleset has a time/ground scale, even if they don't!
Let's take a typical generic "McDonalds" game, that has no time/ground scale.
Typically, rifles fire 24" and infantry move 6" at normal pace. So in a "turn" a infantryman can move about 1/4 of the distance he can fire a rifle. Presuming "effective range" is about 150-300m, we can therefore conclude the timescale for a turn is about a minute or so.
What if the game had infantry move 24" and fire their rifles only 6"? Sounds crazy, doesn't it? But if the timescale was for half hour turns, it makes perfect sense - an infantryman could get well beyond effective rifle range given a half hour head start.
So there is always an implied time scale, even if it is not specifically stated.
What about ground scale? It's dependent on the miniature. Well, for your average 28mm skirmish game it has to be around 28mm/1 inch = ~6ft, give or take a bit. For a 1:3000 warship, 1" might be 250ft.
Now we have a finite amount of tabletop space, so ranges are often "compressed" for shooting. This is to allow units to maneuver more freely without risk of enemy fire , and to make units more "survivable." Sometimes this becomes ridiculous - i.e. a .303 WW2 rifle shoots less than 50 scale metres (150 feet) - aka 24" in a popular set of rules. By their very nature, naval and air games, and definitely space games will have rather more abstract "flexible" distance scales, however.
The miniature scale and terrain dictates the ground scale, which can be altered but should stay within the realms of common sense.
So ground and time scale always exist, even if modern games seem to resolutely refuse to mention them. It's like an elephant in the room.
So why have time and ground scale vanished?
I'm going to borrow some quotes from Rich Clarke (of Two Fat Lardies) which I think points us to the key:-
Having details of unit frontages, formations, tactics, of weapon ranges and rates of march all allows us to create an historically influenced structural framework upon which the rest of the rules will sit.
....Without defining what a unit’s frontage represents (or even what it should be!) we have no point of reference for working out our weapon ranges or movement rates."
A ground scale places annoying constraints on you. Far better to ignore it and do what you want.
A ground scale links to historical accuracy in weapons ranges and movement. Having no fixed ground scale makes it easy to ignore inconvenient info (i.e. the .303 rifle that can't even shoot 50 metres). If your desire is for generic games which share the same mechanisms, weapon ranges and movement rates, then it makes sense to ignore time and ground scale, which might impose some historical accuracy and realism.
Basically, having no scale means the designer can ignore historical accuracy, and thus keep the framework of your "universal gaming system" intact. You CAN use the one ruleset to many wildly different periods - from ancients, to WW2 and sci fi. That's because the rules designer literally altered space and time to make the periods play the same.
Congratulations. You can play the same game with both your medieval crusaders and your ECW musketeers. But why would you want to? It's like playing chess with red and blue instead of black and white pieces. It's still the same game. You've just lost realism, and period "flavour." You now have a bland, generic game with little specific relevance for any time period.
However having similiar rulesets for every period is quite a boon to miniatures manufacturers. They can attract new players from different periods or genres, with the promise that the new period will be easy to learn. Flames of War and Bolt Action have done a great job of siphoning Warhammer 40K players and their cash into historicals.
I don't think it is a coincidence that ground and time scale have vanished at the same time we have more and more generic game engines that boast that they work for all periods. No, the amazing new "universal rule" is not a masterpiece of game design, a one-size-fits-all hat. The game designers have simply just changed the shape of the heads to fit the hat. And now everyone looks the same.