I am not a great candidate for biking so much. I have daycare dropoff and pickup, and also I have bone issues in my ankles that prevent impact type activities like running and biking on hills. Which we have a ton of. (By issues, I mean real ones, as in I wore casts on both legs for most of my toddlerhood and cannot to this day run to save my life. Not bedpan type imaginary wah wah problems.) I can walk forever or bike all day on flat roads and trails though, and love to, and I could get from home to within about 5 blocks of work. But daycare is all hills. Also, if I did bike home for lunch and back, I'd eat up more than half of my lunch hour to do so.
For me, I am not "OH MY GOD, KILLER BEES, HAIR ON FIRE" type of situation financially. I have no consumer debt, a small mortgage, and the stache is growing. I spend about $20 - $25 per week on my commute and those dollars ARE hard at work for me, to earn 5 hours of free time in the evenings with my kid, or in relaxation. For me, biking just isn't a good alternative and I really don't feel guilty about it. I am a conscious and careful user of my gas these days. I am finding lots of other, better-for-me ways to save.
I just wanted the OP to know that they're not the only one who drives home for lunch. :)