On any given realm, you're likely going to see far less leather-workers, which means more opportunity for business. You can monopolize the market easier. The fact of the matter is LW can be a pain to level for some people, and in general more time-consuming to get materials for if you're going about it the traditional way.
The fact that all melee are going to need their leg enchants from you is a big part of business. The leg armors as a result aren't cheap. Depending on your realm, you can get the armors from 500 to 1k gold.
Leatherworking's income is going to remain relatively static because of how few people are willing to actually put in leveling the profession itself, and improved by how much people need the leg armor enchants (and this goes without mentioning any of the Dragon Soul-level gear it can make, which will sell really well, particularly the bracers, of which the craftables tend to be Best In Slot for nearly if not everyone).

By comparison, Glyphs sell singularly for each toon (you don't have to relearn a glyph every time you change which ones you're using, you just have to get dust), with the other available craftables no longer relevant in the later raiding tiers (as mentioned in the article).
I think the Inscription *in general* not making you rich when compared to Leatherworking actually makes a *lot* of sense.