But, seriously... Then isn't the real question: "Why must they learn macro-layout first?"
Why welcome a newbie working on big dev-layout brushes (who doesn't know anything about texturing or detailing) while rejecting those who are learning it from the other direction and dismissing them as "not learning to map" by comparison? Surely you would be equally unsatisfied with those who stop at "orange" maps as much as those never going beyond Valve remakes?
Map makers MAKE maps.
Map makers do not edit maps. Map makers do not make incomplete maps. Map makers make maps that fit the game.
Map makers are artists. Artists do not steal or edit another person's work. Artists might derive work, but always start with a blank canvas.
Map makers are architects. Architects do not copy another's blueprints and change a stairway and market it as their own design. Architects are not interior designers, architects build a structure from the ground up, starting with a foundation.
Map makers are engineers. They draft their own design, they build it using the tools they have. They might re-purpose their own work, but not someone else's.
Map makers are landscapers. They must sculpt the terrain themselves.
This is the way of the map maker.
You would not paint on someone else's work and call yourself a professional artist. You would not modify a set of stairs and call yourself a professional architect. You would not fix a small flaw in someone's draft and call yourself a professional engineer. You would not dig a hole and call yourself a professional landscaper. You would not edit someone else's map and call yourself a map maker.
You would not get a canvas and sketch a design and call yourself a professional artist. You would not lay a foundation and call yourself a professional architect. You would not think of an invention and call yourself a professional engineer. You would not imagine the existence of a hill and call yourself a professional landscaper. You would not release an orange map and call yourself a map maker.
Professionals have standards.
Make your own map.
Make your own map.
And make your own map.
There's little justification in saying that editing a map does you any good. You learn nothing from it you couldn't learn by starting a map from scratch. You learn far less for sure. What can you learn from editing a Valve map? How to make brushes? How to texture? How to place props? That does not compare to the extensive list of things making your own map teaches you: brushwork, layout design, texturing, playtesting and feedback collection, acting on feedback, making changes to improve a layout, displacements, detailing, optimization, soundscapes and ambient effects, spawns, entity systems, lighting, lightmap optimization... the list is endless. These are things a map maker must be knowledgeable in. And editing a Valve map, or releasing an orange map, does not make your knowledgeable on even half the topics which are important to successful map making.
And if you can't make a map, you aren't a map maker.