Your analogy ends short because noone wants thin retaining walls, or - better said - the only one that decides how thick they should be is the calculating civil engineer (that normally does try to optimize thickness of the wall, in order to optimize costs).
An owner/road department might decide to put some limits to the amount of land needed to build the wall and of course there may be particular cases of "narrow" areas, but we are talking of meters (and in my experience there is not that much difference in space needed for excavation between a "basic" and an "exceptionally heavy/thick" retaining wall, the difference may be at the most 1 or 1.5 meter in the base slab), and in these cases one could use gravity walls (that use much more concrete, though with less rebar and usually need less space "behind" for the excavation) or as the original article explaines anchored walls or walls on piles, or even temporary structures (micropiles and anchors usually) only to allow the building of the retaining wall.
The retaining walls (under road) in the first minute of the video are not conventional cantilever retaining walls, BTW, they are one of the common ways "reinforced earth" is made (the typical rebar concrete wall is sketched, as an example, at 10:26) compare these:
https://en.wikipedia.org/wiki/Mechanically_stabilized_earth
they work in a completely different manner, the MSE is more similar to an anchored wall, the "anchors" are in this case pieces of steel strips that resist the pull because of the weight and friction of the earth/soil, if the soil is not suitable or not properly compacted or you introduce a lubricant (water)there is the possibility of these strips to lose adherence, the thickness of the reinforced concrete outer slabs is irrelevant and usually fixed, independent from height of the wall or other local conditions, if I recall correctly some 14 cm.
Anecdotally, I have built both kinds of walls, and actually also once "saved" a piece (some 40 or 50 mt long) of MSE-like wall that was failing (though due to other reasons, the foundation was underdimensioned), the huge difference is that traditional retaining walls are "independent" from the soil you put behind it (as long as it is within a normal weight of 1,600-2,100 kg/m3) while the MSE stability depends greatly on the quality of the soil and the way it is compacted (besides a valid calculation of the length of the strips).
As a side note, MSE-like walls are usually perfectly vertical (and actually do seem like falling inward optically when they are high).
An owner/road department might decide to put some limits to the amount of land needed to build the wall and of course there may be particular cases of "narrow" areas, but we are talking of meters (and in my experience there is not that much difference in space needed for excavation between a "basic" and an "exceptionally heavy/thick" retaining wall, the difference may be at the most 1 or 1.5 meter in the base slab), and in these cases one could use gravity walls (that use much more concrete, though with less rebar and usually need less space "behind" for the excavation) or as the original article explaines anchored walls or walls on piles, or even temporary structures (micropiles and anchors usually) only to allow the building of the retaining wall.
The retaining walls (under road) in the first minute of the video are not conventional cantilever retaining walls, BTW, they are one of the common ways "reinforced earth" is made (the typical rebar concrete wall is sketched, as an example, at 10:26) compare these: https://en.wikipedia.org/wiki/Mechanically_stabilized_earth
https://reinforcedearth.com/products/retaining-walls/mechani...
with a "normal" retaining wall like the gravity and cantilever sketched here:
https://en.wikipedia.org/wiki/Retaining_wall https://en.wikipedia.org/wiki/File:Retaining_Wall_Type_Funct...
they work in a completely different manner, the MSE is more similar to an anchored wall, the "anchors" are in this case pieces of steel strips that resist the pull because of the weight and friction of the earth/soil, if the soil is not suitable or not properly compacted or you introduce a lubricant (water)there is the possibility of these strips to lose adherence, the thickness of the reinforced concrete outer slabs is irrelevant and usually fixed, independent from height of the wall or other local conditions, if I recall correctly some 14 cm.
Anecdotally, I have built both kinds of walls, and actually also once "saved" a piece (some 40 or 50 mt long) of MSE-like wall that was failing (though due to other reasons, the foundation was underdimensioned), the huge difference is that traditional retaining walls are "independent" from the soil you put behind it (as long as it is within a normal weight of 1,600-2,100 kg/m3) while the MSE stability depends greatly on the quality of the soil and the way it is compacted (besides a valid calculation of the length of the strips).
As a side note, MSE-like walls are usually perfectly vertical (and actually do seem like falling inward optically when they are high).