Why were construction companies caught in the credit crunch?

That's my question. Years ago I went to a Midlands construction company to prospect them for business, and learned that they had a long-term strategy of buying land when the market was depressed and developing it when the upturn came (well, duh, you're saying, doubtless). They'd done this for several business cycles, as (I assume) any well-established firm in their sector would have done.

It was obvious to me ages ago that house prices had gotten silly. How did major building companies get it so wrong this time, when watching the trend is so fundamental to their survival?