I CONFESS I planted in the same bed as last year, when the plants were huge and healthy. Could this be the problem -- not rotating?

Yes.

Or maybe not.

Some things to think about:
-- Did you mix in compost before planting? If not, in future seasons, mix in at least two inches.
-- Did you water adequately? Or too much?
-- When you remove the plants this year, dig them up so that you can check the roots for problems.

I am just starting to work my way through the tomato info. here, but my tomatoes all ended up like Annie's this year. I am in Riverside, CA.

I planted in a new area this year. I was wondering if the problem could have been from using cages that weren't cleaned well?

Last year was my first year growing tomatoes. They did well, but once school started they were neglected and just sat there dying agonizing deaths for months.