Its simple priorities. I come home from work. After I go for a run, make dinner, change clothes etc, I've got 4-5 hours spare. But hey, maybe my friends want to meet me in town for a drink or two. Or my housemates want to watch a few episodes of that TV series we're in the middle of. Or I just wanna unwind and play other video games, or read a book, or...
Sure I might feel like a good 3-4 hour raid the odd time. But that's not gonna be enough to satisfy any half decent raiding guild that I could apply to.