Who says this character is the first? Maybe they think they are but they're wrong. Why did those who proceeded this character fail?
Admittedly, I was assuming one of the more basic tropes of fantasy RPGs - the rules of magic, and the state of the world are eerily static. Sure, the rulers of nations, and national boundaries, change, but the fundamentals of magic and economics are pretty much unchanging. And, in such a scenario, if the scheme could work, by the rules, there are so many chances over the decades and centuries for someone to think of it that... it should have been thought of several times over.
And, like the assembly line - you only need one to make it work for it to rather quickly become the way business is done. It starts to stretch credulity that over the generations, it didn't become commonplace. If the rules actually allow it, "Why did the several hundred other people fail" becomes
harder to answer than, "Why did nobody else think of this before?"
In D&D, the answer is simple - the scheme doesn't actually work. Each 5th level or higher wizard who can cast the spells can only manage a couple of undead. And those undead, being mindless, are really only good for very basic manual labor. The value of the labor from a couple of undead is very small compared to the value that wizard can get out of something other than managing menial labor.
I expect this will be true for most RPGs. The games exist to tell tales of action and adventure, for the most part, not tales of working out the economics and bookkeeping of investment in the undead-labor industry.
However, let us assume the game mechanics do allow it. Both questions ("Why didn't anyone else do this, or why did they fail?") are answered by another major fantasy trope - mucking about with the dead is not socially acceptable. Like,
really not acceptable. Like, burning at the stake level of unacceptable. No matter how much more efficient undead may be, nobody can afford to risk using them, for they'd be out of business and possibly executed for their trouble.
This changes the goal of the PC. It becomes not a question of
efficiency, and instead becomes an effort to trying to convince the culture that mucking with undead isn't an issue.