Actually, we don't have enough classes for Lone Wolf. The entire idea of Lone Wolf, unlike stock d20 fantasy, is that each class grants its own set of features and powers based on its background and region, unlike the more generic D&D sets topped off with prestige classes and races. This is a fairly new concept for d20, as most fantasy settings are designed for traditional integration of D&D classes and then adapt them via some rule set changes or explanations of how they work in that fantasy setting.
Non-human races are not very present in Lone Wolf due to the destruction of most of them by the great Plague released by the Cener. Only the Drodarin Dwarves, Giants, the Kundi, and the Ogrons remain as a real example of the wide range of non-human races created by Kai. You have a couple of other examples in the Noondnics (halfing rats) and the Crocaryx living in the city of Nyaxtor or under the control of the Darklords, but that's it.
Therefore, in order to provide variety for the d20 player not used to the setting or as a reflection of the varying levels of knowledge older gamebook players have, classes for humans become the best way of providing variation between players. All of the classes presented in the books are a representative of varying members of the world you meet as Lone Wolf, and it makes far more sense to provide such a range to keep players interested.
On the adventure side, the legagcies of the non-human races provide a large source of roleplaying potential and suprise. Any material from any d20 fantasy article or setting can be added to Lone Wolf with some conversion, as long as it fits YOUR sense of the game. That is the other problem many people have with the interlocking nature of d20. They see outside sources as dangerous influences that players want to try out because they see this new article or supplement as cool. If a player wants to try out a new class or supplement, take a look at and see if it fits into your setting and current campaign. If not, say no and continue with the game as you see fit.