Actually, I believe that, over time, the players are conditioned by the experiences they have with various GMs to regard certain alignments as desirable and others that are not. Most often, one group of players I know usually (given a choice) invariably trends toward playing true neutrally-aligned characters. The popular explanation for this phenomenon as it has been explained to me is that the alignment of "neutral" as defined in the PHB is closest to what they believe is the moral and ethical viewpoint of modern-day individuals like themselves. Of course, IMHO, since the majority also play or have played Shadowrun (touting it as their favorite or second favorite system/setting), the mindset common to veteran SR players overlaps into the way the same players create characters for D&D, i.e., as shadowrunners in a pure fantasy setting, which results in the quality of self-interest being present in the character profile to a significant degree..."let's get paid."
Because D&D in its past and present forms encourages the advancement of characters through accumulating wealth and killing monsters, it stands to reason that the good alignments are less desirable for play, as neutral characters don't *have* to think about the moral quandries good characters would sometimes find themselves encountering in pursuit of the same goals. Evil characters don't have to think about it at all, and their alignment encourages that thought process.
I used to play good characters in a group of neutrally-aligned PCs, but inevitably, I evolved away from doing so to minimize internal party conflict. I only play good characters in a group where I have at least a couple of potential allies rooted in common cause.
I would recommend that GMs desiring to condition their troupe of players to select good alignments on their own accord consider implementing the following system:
Show the *benefits* of being good-aligned within the setting and the campaign!
Off the top of my head, let the good-aligned characters receive bonuses on reaction rolls with NPCs...that is if the players are playing true to alignment. This can be rationalized by the NPCs picking up a "vibe" off of the PC that encourages interaction and empathy. Simplistic, but kind of the direction you want to go to accomplish the goal.
Better yet, ask your players' opinions. See if there is anything you can do to tweak the way players of good PCs receive a sense of reward without encouraging the mercenary aspects.
My two cents.
