Wherefore, oh veggies?

I see a month ago I had my fall veggies planted and some sprouted.  Why is it that nothing grew?  Beets especially need to be in the ground 12 weeks before first frost.  I did that.  Either none came up, or they did, only to be eaten or killed by the heat.  I have resown this week, but who knows if anything will come of it?  Is it worth it?  I am not sure.  I bought a pack of cucumbers and got several quite long ones, Japanese this year, but the vines shriveled while I was gone so that season is over.  So, say $2.49 for a six pack of cucumber plants and I got three or four cucumbers.  At the farmer's market they are about a dollar each, so yeah, maybe it was worth it, in that sense.  But why oh why can't I grow veggies?