Don't know the reasons, but at the time they had it I think the tickets were about $20 (maybe less I don't remember anymore). I think part of it was that a lot of the theme parks around here have scary halloween nights and they didn't go that route. Probably there weren't enough parents willing to bring their kids (we went both years and usually it was a group of mostly 20 somethings with a few teenagers and 1 kid, so we had about 8 or 9 adults and 1 kid with us)
Also DL stays open till 8pm on off season now. In order to do it they'd have to scale there hours back to at least 6 and probably earlier. Since mostly who would go are kids, and school is in session parents don't want their kids out late, and they always had it during the week if I remember correctly.
Another big difference is that DLs guest are mostly locals with a lot of those being AP holders, wheras WDWs are more visitors from other areas, so what people do once they may not be willing to do again. I'm guessing the expense of having to have yet another shift of people for the parties was worth the amount of money they were bringing in.