They did do FPGA, many of the companies selling FPGA boards to mine have ceased operations because interest has dropped off since ASICS are where it is at now.

FPGAs are the same speed as GPUs but cost more, so they're only better if you're paying a lot for power.

The advantage to FPGAs is that they can be designed rapidly. ASICs are cheaper to manufacture and usually run faster.

Actually, if you were serious about mining, FPGAs might still be a good choice. They are approximately as efficient as current ASICS, just much slower. Plus they will have resale value.