Well, I had thought the reason was because we already have a fairly large number of races, 15 including the race Torack just created, that is a lot of different races. If race creation is allowed to go on indefinitely, then things will get quite cluttered, and the RP would be in a state of constant flux, not to mention the large amount of material would make it harder for new players to jump in. At this point it would be perhaps better if the world itself, and the current existing races were expanded upon, rather than adding in more new races.
Though perhaps a compromise of sorts is in order. This is just an idea. Put each race in one of two categories, Major races, and Minor Races. Major races would be those races whose numbers are large enough to warrant being on the map, and being necessary to read about. There would be a limited amount of Major Races.
Minor races can be those races who aren't that numerous etc etc, and can be skipped until circumstances require reading their sheet. There could perhaps be an indefinite number of them, or a higher limit than the limit of the Major races.
Current RP - 850
Recruits - 400
Companies - 0
GENERATION 13: The first time you see this, copy it into your sig on any forum and add 1 to the generation. Social experiment.