Some of these reasons have been stated elsewhere. But as one of the frustrated fans behind the Raines for Hall of Fame site Raines30.com, they bear repeating, because Hall of Fame voters are completely missing the boat.
1) If Raines played his whole career with the Yankees or Red Sox and not the Expos, he'd be in already and we wouldn't be having this discussion. Gary Carter went through the same thing for several years, and he was one of the greatest catchers of all-time and shoiuld have been automatic, an absolute lock.
2) The voters are missing how unreal Raines' career OBP (.385) was, as well as his how great his SB (804) and especially SB success rates were (84|PERCENT|+, the best ever for someone with anywhere near that many attempts). While many writers pay lip service to how much they enjoy nuanced baseball instead of swinging for the fences, when it comes to things like MVP and HoF votes, they miss the big picture if they don't see either big HR/RBI totals, or the requisite 3,000 hits.
As an aside, here's a fun fact: Tim Raines reached base more times in his career than Tony Gwynn did. But because Gwynn hit more singles and Raines had more walks, Gwynn gets in on the first ballot and Raines...well, who knows. Raines hit .294 for his career and totaled 2,605 hits. Replace 20 walks a season in Raines' career with 20 singles a year and his value barely changes at all. Yet he's then a .300 career hitter and a 3,000 hits guy, and would already be in the Hall.
3) Related to #2, the voters hold Raines' lack of MVP votes against him. Which is ridiculous. He should have been a top candidate for MVP pretty much straight through the mid-80s. Even missing a month in '87 (due to collusion, not his fault) you could build a case for him to win the award...he certainly delivered more value that season that Hawk did. Anyway, the same people who fail to appreciate Raines' value in an MVP vote now double-penalize him for their own short-sightedness 20-25 years ago.
4) I do think there's at least a tinge of racism going on, even if it's unconscious racism. Keith Law has an excellent take on this last factor (http://sports.espn.go.com/mlb/hof09/columns/story?columnist=law|UNDER|keith&id=3825493), as it pertains to Raines' drug use. I'd rank the other three factors much higher on the list of likely reasons for exclusion. But this is in there somewhere too.
5) This whole idea of protocol, who goes when and who has to wait their turn. It's possible that Raines might get in some time in the future, when there's a weaker field competing against him (Bert Blyleven, Mark McGwire and Alan Trammell would have gotten in this year too if I were voting, with Jim Rice out–and I'd have resurrected Lou Whitaker and Bobby Grich and given them consideration too). This is another stupefyingly dumb idea. If there are five, six, eight guys who deserve to be inducted, they should be inducted. Voters' self-imposed constraints of only voting in a certain number of players per year, regardless of the field's credentials, drives me nuts. It won't be a huge deal if Raines gets in at some point in the future (other than making a worthy candidate wait several years for no reason). But if the fickle voters carry this out for 15 years, it'll be up to the Veterans Committee (another dodgy bunch) to give Raines his due. Ugh.