A few things:
a) For smaller companies, French versions may exists, MONTHS after the original exists. Right now, it's somewhat fuzzy on whether if that happens, do they have to re-release a French version here.
b) If the answer is yes, there will be additional work. EU versions of games are typically a different build than the NA versions. In order to facilitate a French version for North America, either 1)They have to submit a second version to the console manufactures/ESRB to be retested (and have a seperate SKU, licensing and cost associated with it) or 2)Push the NA version to have French built in to begin with.
The problem here is that both cases will have their drawbacks.: 1) requires additional cost, and depending on the title, and the market it's for, may not be worth it for some companies (whereas it is still viable in EU regions, when multiple languages are on the same cart/disk). 2) Incurs an extra delay across the board for all of North America, and can potentially run into storage limitation (most noticable in DS games, where typical EU region games have to include multiple language images for textures, etc).
You're right, for the most part, this should not be a problem, for most games, but it doesn't mean it's not a problem ever for everyone.