The way I saw it, SPLC didn’t declare FRC a hate group until 2010 because they didn’t have the confidence to do so before then. I believed the situation evolved with the Obama Administration and various advances of the gay rights movement. It seems the “hate group list” was a new tactic in terms of traditional and Christian groups and was also spurred by NOM (National Organization for Marriage).
Yes, the 2010 elections may have had something to do with the timing as well.
In any case, SPLC issued their Special Intelligence Report in the winter of 2010:
“18 Anti-Gay Groups and Their Propaganda”
Addendum:
I meant gay advocacy’s sparring with NOM’s Brian Brown spurred SPLC on to create the hate list; or it seemed to happen in tandem with it.